The operation of thermal power plants involves the use of large amounts of water. The main part of water (more than 90%) is consumed in cooling systems of various devices: turbine condensers, oil and air coolers, moving mechanisms, etc.
Wastewater is any stream of water removed from a power plant cycle.
Waste or waste water, in addition to water from cooling systems, includes: waste water from hydroash collection systems (HSU), spent solutions after chemical washing of thermal power equipment or its conservation: regeneration and sludge water from water purification (water treatment) plants: oil-contaminated wastewater, solutions and suspensions, arising when washing external heating surfaces, mainly air heaters and water economizers of boilers burning sulfur fuel oil.
The compositions of the listed wastewater are different and are determined by the type of thermal power plant and main equipment, its power, type of fuel, composition of the source water, method of water treatment in the main production and, of course, the level of operation.
Water after cooling the condensers of turbines and air coolers, as a rule, only carries so-called thermal pollution, since its temperature is 8...10 C higher than the temperature of the water in the water source. In some cases, cooling waters can introduce foreign substances into natural bodies of water. This is due to the fact that the cooling system also includes oil coolers, a violation of the density of which can lead to the penetration of petroleum products (oils) into the cooling water. At fuel oil thermal power plants, wastewater containing fuel oil is generated.
Oils can also enter wastewater from the main building, garages, open switchgears, and oil facilities.
The amount of water in cooling systems is determined mainly by the amount of exhaust steam entering the turbine condensers. Consequently, most of this water is at condensing thermal power plants (CHPs) and nuclear power plants, where the amount of water (t/h) cooling turbine condensers can be found by the formula Q=KW Where W- station power, MW; TO-coefficient for thermal power plants TO= 100…150: for nuclear power plants 150…200.
In power plants using solid fuels, removal of significant quantities of ash and slag is usually carried out hydraulically, which requires large quantities of water. At a thermal power plant with a capacity of 4000 MW, operating on Ekibastuz coal, up to 4000 t/h of this fuel is burned, which produces about 1600...1700 t/h of ash. To evacuate this amount from the station, at least 8000 m 3 /h of water is required. Therefore, the main direction in this area is the creation of circulating gas recovery systems, when clarified water freed from ash and slag is sent back to the thermal power plant into the gas recovery system.
The waste waters of gas treatment facilities are significantly contaminated with suspended substances, have increased mineralization and, in most cases, increased alkalinity. In addition, they may contain compounds of fluorine, arsenic, mercury, and vanadium.
Effluents after chemical washing or conservation of thermal power equipment are very diverse in composition due to the abundance of washing solutions. For washing, hydrochloric, sulfuric, hydrofluoric, sulfamic mineral acids are used, as well as organic acids: citric, orthophthalic, adipic, oxalic, formic, acetic, etc. Along with them, Trilon B, various corrosion inhibitors, surfactants, thiourea, hydrazine, nitrites, ammonia.
As a result of chemical reactions in the process of washing or preserving equipment, various organic and inorganic acids, alkalis, nitrates, ammonium salts, iron, copper, Trilon B, inhibitors, hydrazine, fluorine, methenamine, captax, etc. can be discharged. This variety of chemicals requires a customized solution for neutralizing and disposing of toxic chemical wash waste.
Water from washing external heating surfaces is formed only at thermal power plants using sulfur fuel oil as the main fuel. It should be borne in mind that the neutralization of these washing solutions is accompanied by the production of sludge containing valuable substances - vanadium and nickel compounds.
During the operation of water treatment of demineralized water at thermal power plants and nuclear power plants, wastewater arises from the storage of reagents, washing of mechanical filters, removal of sludge water from clarifiers, and regeneration of ion exchange filters. These waters carry significant amounts of calcium, magnesium, sodium, aluminum, and iron salts. For example, at a thermal power plant with a chemical water treatment capacity of 2000 t/h, salts are discharged up to 2.5 t/h.
Non-toxic sediments are discharged from pre-treatment (mechanical filters and clarifiers) - calcium carbonate, iron and aluminum hydroxide, silicic acid, organic substances, clay particles.
And finally, in power plants using lubrication and control systems steam turbines fire-resistant liquids such as ivviol or OMTI, a small amount of wastewater contaminated with this substance is generated.
The main regulatory document establishing the security system surface waters, serve as “Rules for the protection of surface waters (standard regulations)” (M.: Goskomprirody, 1991).
INFORMENERGO
Moscow 1976
This “Manual” was developed by the All-Union State Design Institute of the Order of Lenin and the Order of the October Revolution “Teploelektroproekt” and is mandatory for use in the design of newly built and reconstructed thermal power plants.
The “Guide” was developed as a follow-up to the “Temporary Guidelines for the Technological Design of Facilities for the Treatment of Industrial Wastewater from Thermal Power Plants,” which have become invalid since October 1976.
The “Guide” has been agreed upon with the Ministry of Land Reclamation and Water Resources of the USSR, the Glavrybvod of the Ministry of Fisheries of the USSR, and the Ministry of Health of the USSR.
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1. General part. 1 2. Cooling system wastewater. 3 3. Wastewater from hydroash and slag removal systems (HSU) 4 4. Washing waters of regenerative air heaters and convective heating surfaces of boilers operating on fuel oil. 5 5. Waste water from chemical washing and equipment preservation. 7 6. Waste water from water treatment and condensate treatment. eleven 8. Wastewater contaminated with petroleum products. 12 9. Wastewater from hydraulic cleaning of fuel supply tract premises. 15 10. Rainwater from the territory of the power plant. 16 Application. Calculation of the amount of purging of the GZU system.. 16 |
1 . a common part
1.1. The “Guide” applies to the design of structures intended for the treatment and purification of wastewater generated in the production processes of thermal power plants:
contaminated with petroleum products;
from hydraulic cleaning of fuel supply tract premises;
rainwater from power plant areas.
The design of structures for the disposal and treatment of domestic wastewater from thermal power plants and residential settlements is carried out in accordance with SNiP II-32-74 “Sewerage. External networks and structures.”
1.2. When designing industrial sewerage and wastewater treatment and treatment facilities, it is necessary to consider:
the possibility of reducing the amount of contaminated industrial wastewater through the use of advanced equipment and rational circuit solutions in the technological process of a thermal power plant;
use of partially or fully recycled water supply systems, reuse of waste water in one technological process in other installations;
eliminating the discharge of uncontaminated wastewater into water bodies and using it to replenish losses in circulating water supply systems;
the possibility and feasibility of obtaining and using thermal power plants or needs for one’s own needs National economy valuable substances contained in industrial wastewater;
the possibility of extremely reducing or completely eliminating the discharge of wastewater into water bodies, using waste water for the TPP’s own needs;
the possibility of using existing, designed treatment facilities of neighboring industrial enterprises and settlements or constructing common facilities with proportional share participation.
1.3. The choice of method and scheme for processing industrial wastewater is made depending on the specific conditions of the designed power plant: power and installed equipment, operating mode, type of fuel, method of ash and slag removal, cooling system, water treatment scheme, local climatic, hydrogeological and other factors, with the corresponding technical and economic justifications.
1.4. Facilities for the treatment and purification of industrial wastewater from thermal power plants, as a rule, should be arranged in one block, and the possibility of their cooperation with technological water treatment should also be considered.
1.5. When designing facilities for the treatment and purification of industrial wastewater, the following regulatory documents should be used:
“Additional list of maximum permissible concentrations of harmful substances in the water of reservoirs for sanitary and domestic water use” - No. 1194, 1974.
“Guidelines for State Sanitary Inspection Bodies on the Application of the Rules for the Protection of Surface Waters from Pollution by Sewage.”
SNiP II-32-74 “Sewerage. External networks and structures", 1975
SN-173-61 “Guidelines for the design of external sewage systems for industrial enterprises.” Part 1, 1961
SNiP II-31-74 “Water supply. External networks and structures", 1975
1.6. The discharge of wastewater into reservoirs and watercourses must be designed in compliance with the “Rules for the protection of water surfaces from wastewater pollution” and, in accordance with the established procedure, be coordinated with the authorities for regulating the use and protection of water, the State Sanitary Inspection, for the protection of fish stocks and regulation of fish farming and other interested authorities .
2 . Wastewater system e we are cooling
2.1. Cooling system wastewater discharged after turbine condensers, gas coolers, air coolers, oil coolers and other heat exchangers, where the source water is only heated but is not contaminated with mechanical or chemical impurities, does not require treatment.
2.2. The discharge of water heated at the power plant into reservoirs and watercourses for drinking, cultural, domestic and fishing water use is carried out on the basis of the general requirements of the “Rules for the Protection of Surface Waters from Pollution by Sewage”, 1975.
Note. Calculation justifications should be carried out based on the following. The average monthly water temperature at the design site of a reservoir for domestic, drinking and cultural water use in the summer after the discharge of heated water should not increase by more than 3 °C compared to the natural average monthly water temperature on the surface of the reservoir or watercourse for the hottest month of the year 10% probability . For fishery reservoirs, the water temperature at the design site in summer should not increase by more than 5 °C compared to the natural temperature at the water outlet. The average monthly water temperature of the hottest month in the design area of fishery reservoirs should not exceed 28 °C in a hot year of 10% supply, and for reservoirs with cold-water fish (salmon and whitefish) should not exceed 20 °C.
The water temperature in the design area of fishery reservoirs in winter should not exceed 8 °C, and in burbot spawning areas 2 °C.
2.3. To ensure the required level of water temperatures in reservoirs for drinking, cultural, domestic and fishery water use with direct-flow and recirculating cooling systems with reservoirs, it is recommended to use:
deep water intakes from stratified reservoirs and surface water outlets, which makes it possible to reduce the temperature of the intake and, accordingly, discharge water compared to the surface temperature of the reservoir;
spray installations above the water area of the outlet channels or reservoir for pre-cooling and aeration of water before discharge into a public reservoir;
increased steam cooling rate in winter;
ejecting water outlets, providing 1.5 - 3.0-fold mixing of waste water with reservoir water in the spillway area under appropriate hydrological, geomorphological and economic conditions;
ice-thermal installations under appropriate climatic conditions, when economic justification confirms the feasibility of their use.
2.4. When using bulk reservoirs, lakes and reservoirs that do not have economic or cultural significance as cooling reservoirs, the thermal regime is determined by the optimal operating conditions of the power plant. In these cases, in accordance with the “Fundamentals of Water Legislation of the USSR and Union Republics,” the power plant’s right to separate use of the reservoir is formalized.
2.5. To ensure the maximum technically possible vacuum in turbine condensers and to prevent contamination of heat exchange surfaces in direct-flow and recirculating cooling systems with reservoirs, mechanical water purification should be used.
When using mesh filters, the size of the mesh cells should not exceed 2×2 mm.
The water velocities in the heat exchanger tubes should not be lower than 1.0 m/s.
It is recommended to prevent slimy (including biological) deposits on condenser pipes by continuous cleaning with rubber balls or periodic chlorination.
In recirculating cooling systems with cooling towers and spray pools, as measures to prevent scale formation on condenser tubes, it is recommended to use purging, acidification, phosphating, joint acidification and phosphating of water, and also, as they are mastered, reagent-free methods of water treatment (magnetic, ultrasonic, etc. .).
2.6. Blowing water from circulating cooling systems with cooling towers and spray basins should be used as much as possible to power water treatment, replenish the gas and water supply system, water the irrigation area of agricultural land and for other on-site and economic needs. Excess blowdown water is discharged into water bodies with concentrations of pollutants within the limits permitted by the “Rules for the protection of surface waters from pollution by wastewater.”
2.7. It is recommended to determine the chemical composition of the blowdown waters of circulating cooling systems using the “Methodology for compiling hydrochemical forecasts taking into account the scale-forming properties of cooling water of thermal power plants,” developed by the ORGRES trust in 1975.
3 . Wastewater from hydroash and slag removal systems (HSU)
3.1. Water supply to GZU systems, as a rule, is designed according to a reversible scheme, with the reuse of water for hydraulic transport of ash and slag (return GZU system). Water supply to GZU systems using a direct-flow scheme, as well as partial discharge of water from GZU systems into water bodies (purging to regulate the salt composition of water in the GZU system) can only be used in exceptional cases and upon agreement of the conditions and time of discharge with the State Sanitary Inspection authorities, according to regulation of water use and protection, protection of fish stocks and regulation of fish farming.
3.2. When designing a circulating water supply system, a water balance is drawn up, revealing a shortage or excess of water in the system.
The water balance of the gas treatment system, as a rule, should be designed to be deficient or zero.
3.3. The need to purge the circulating system of the gas charger is determined by calculation (see appendix).
In addition to the direct discharge of blowdown water into water bodies, subject to the conditions specified in clause 3.1, the following directions for disposal of blowdown water should be considered:
irreversible use of blowdown water in the technological cycles of the power plant;
evaporation of purge water using special devices;
others, determined by the specific conditions of a given power plant.
3.4. When the water balance is deficient, the system is replenished with contaminated industrial wastewater from thermal power plants. The admissibility of supplying saline wastewater to the gas treatment system is determined by calculation.
3.5. In order to reduce the water balance to deficient or zero, the following should be provided:
interception and diversion of surface runoff from its catchment area bypassing the ash dump;
the use of devices to increase water losses due to evaporation in an ash dump (distributed release of pulp onto ash and slag beaches, irrigation of beaches with clarified water, etc.);
the use of clarified water for extraction and compaction in the bearings of slag and slurry pumps, washing of ash and slag pipelines, maintaining the water level in the suction pits of slag and slurry pumps and for other purposes. The use of fresh process water for these purposes is prohibited.
3.6. With a reversible GZU system, wet ash collectors should be irrigated with clarified water. Is water with a pH suitable for irrigation? 10.5 and containing less than 36 mEq/L of sulfates. If the clarified water does not meet these parameters, the system provides a device for treating the clarified water supplied for irrigation of wet ash collectors.
It is necessary to consider the feasibility of using contaminated industrial wastewater from thermal power plants for scrubber irrigation. To do this, you can use wastewater contaminated with petroleum products without treatment, as well as chemically contaminated wastewater after its pre-treatment.
The use of wet ash collectors for ash with high alkalinity must be justified by making a technical and economic comparison with dry ash collectors, and the costs of treating clarified water required for its use to irrigate wet ash collectors must be taken into account, and if purging is necessary, the costs associated with it must be taken into account.
3.7. When designing ash and slag dumps, protection of surface and groundwater from pollution must be provided; relevant water protection measures must be coordinated in accordance with the established procedure with the bodies of the Ministry of Geology and bodies regulating the use and protection of water.
4 . Washing waters of regenerative air heaters and convective heating surfaces of boiler units operating on fuel oil
4.1. It is necessary to provide for the neutralization and neutralization of toxic substances contained in wastewater from washing RVP and convective heating surfaces of boilers operating on fuel oil. Discharge of this group of waters into reservoirs without neutralization and detoxification of toxic substances is unacceptable.
4.2. When designing a unit for the neutralization and neutralization of these waters, one should be guided by the following data:
a) for washing the RVP take:
the amount of washing water is 5 m 3 per 1 m 2 of the rotor section;
washing duration - 1 hour;
Washing frequency is once every 30 days.
The total amount of washing water for RVPs of various diameters should be taken according to the table. 1.
Table 1
b) for washing the convective heating surfaces of the boiler unit, take:
washing frequency once a year before repairs;
washing duration - 2 hours;
water consumption for washing a boiler with a steam capacity of 320 t/h or more is 300 m 3.
c) for washing peak boilers, take:
the average frequency of washing is once every 15 days of operation;
Washing duration is 30 minutes.
The water consumption for washing boilers of various types is:
For peak boilers equipped with shot blasting cleaning of heating surfaces, the washing frequency should be once a year.
4.3. The calculated composition of the washing waters of both RVP and fuel oil boiler units should be taken according to table. 2.
table 2
4.4. When designing a unit for the neutralization and neutralization of washing water, it is necessary, as a rule, to provide for the deposition of vanadium-containing sludge that meets the requirements of metallurgical plants. This condition corresponds to the neutralization of washing water in two stages:
the first is the treatment of water with caustic soda to a pH value of 4.5 - 5 for the precipitation of vanadium oxides and the separation of vanadium-containing sludge on filter presses of the FPAKM type;
the second is the treatment of water clarified after the first stage with lime to a pH value of 9.5 - 10 - for the precipitation of oxides of iron, nickel, copper, as well as calcium sulfate.
4.5. The estimated consumption of reagents for neutralizing washing water is:
caustic soda in the first stage - 6.0 kg/m 3 in terms of NaOH;
lime in the second stage - 5.6 kg/m 3 in terms of CaO.
4.6. The volume of liquid sludge in the neutralizer tank after 5-6 hours of sediment settling in the first stage is taken equal to 20% of the initial volume of washing water, and the solid content in it is equal to 5.5%.
The volume of liquid sludge in the neutralizer tank after 7-8 hours of sediment settling in the second stage is taken equal to 30% of the initial volume of clarified water in the first stage, and the solid content in it is equal to 9%. When neutralizing water with industrial lime, the solid content in the sediment should be taken into account the ballast in the milk of lime.
4.7. Liquid sludge after the first stage is sent to a special sludge collection tank.
The tank is equipped with a recirculation pipeline to obtain sludge of uniform concentration and supply it to the filter press. The sludge obtained after filtering is packed into bags, stored and sent for processing to metallurgical plants.
Temporarily, in the absence of filter presses, a container with a non-filterable base is provided to store sludge from the first stage of neutralization for 5 years.
4.8. Neutralization of washing water in two stages should be provided in various neutralizing tanks in order to obtain purer vanadium-containing sludge.
4.9. Liquid sludge after the second stage of neutralization must be sent to a sludge dump with an impervious coating device, the capacity of which is calculated for 10 years of operation of the thermal power plant at full design capacity.
4.10. After the second stage of neutralization, clarified water is sent for reuse for washing RAH and convective heating surfaces of boiler units. This system is purged with water, which transports the sludge to the sludge dump. After settling, the water is supplied to the saline wastewater stream in accordance with paragraph 6.7.
4.11. The average composition of neutralized washing water should be:
pH - from 9.5 to 10; CaSO 4 content - up to 2 g/l.
4.12. The average composition of sludge after neutralization should be taken according to table. 3.
Table 3
4.13. Each neutralizer tank must contain washing water from washing one RVP and reagents for their neutralization. The number of neutralizer tanks at thermal power plants should be no less than two and no more than four, depending on specific conditions.
4.14. When washing peak boilers at pulverized coal-fired thermal power plants, it is allowed to neutralize the washing water with lime. Neutralized water together with sludge can be sent to the hydraulic ash removal system if the pH of clarified water is not lower than 7. If the pH of clarified water is below 7, it is necessary to provide a separate sludge storage tank.
4.15. The estimated consumption of lime when neutralizing washing water according to paragraph 4.14 is 7 kg/m 3 in terms of CaO.
4.16. Anti-corrosion protection must be provided for containers for collecting and neutralizing washing water, as well as pipelines for supplying washing water to the neutralization unit.
The containers are equipped with recirculation pumps, air distribution and reagent supply.
Pumps for pumping and recycling neutralized water must be acid-resistant.
5 . Waste water from chemical washing and equipment preservation
5.1. The design of devices for treating waste water should be based on the methods of pre-start and operational chemical treatment used:
a solution of inhibited hydrochloric acid;
a solution of sulfuric or hydrochloric acid with hydrazine;
phthalic anhydride solution;
a solution of dicarboxylic acids;
a solution of low molecular weight acids (NMK concentrate);
monoammonium citrate solution;
solution based on complexones.
5.2. It is prohibited to use reagents for washing and preserving thermal power equipment for which maximum permissible concentrations (MPC) in water bodies have not been established, as well as reagents that cannot be neutralized or converted into substances for which MAC values have been established.
5.3. To protect equipment from parking corrosion, “wet” preservation methods are used, which consist of filling the boiler unit with solutions of hydrazine or atmospheric corrosion inhibitors, or a mixture of ammonia and sodium nitrite. The frequency of conservation is determined by the operating mode of the equipment. To neutralize and neutralize spent preservative solutions, it is necessary to use installations for neutralization and neutralization of waste water from chemical treatment.
5.4. To determine the amount of waste water, proceed from the following possible chemical treatment operations:
a) water washing with industrial water;
b) degreasing internal surfaces with alkali or OP-7 (OP-10) in a closed circuit;
c) displacing the solution with industrial water and then replacing it with desalted water;
d) acid washing in a closed circuit;
e) displacing the solution and water washing with industrial water (with the addition of alkaline reagents) and then replacing it with desalted water;
f) passivation of cleaned surfaces in a closed loop;
g) drainage or displacement of the passivating solution with demineralized water.
Notes.
1) When carrying out degreasing according to point “b” with a solution OP-7 (OP-10) of once-through boilers, this operation is combined with acid washing without intermediate displacement of the solution.
2) For drained boilers, according to point “g”, the passivating solution is drained, and water washing is carried out before starting the boiler.
3) When carrying out two-stage washings, the operations under points “d” and “e” are repeated after the operation under point “d”.
4) When carrying out operational chemical cleaning of heating surfaces of once-through boilers with solutions based on complexones, waste water is formed only in operations according to points “d” and “e” without the use of washing with industrial water.
5.5. The collection and neutralization of spent washing solutions should be provided in neutralizing tanks, the volume of which should be designed to receive acidic and alkaline solutions, taking into account their threefold dilution with water when displaced from the circuit. Acidic and alkaline washing solutions collected in neutralization tanks should be used for mutual neutralization.
The capacity of the neutralizer tanks must be at least seven times the volume of the circuit to be flushed for one-stage flushing and ten times the volume for two-stage flushing, guided by the data in Table. 4.
5.6. To collect wastewater from water washes of equipment, as well as lightly contaminated wastewater (PH = 6 - 8) from the displacement of acidic and alkaline solutions, it is necessary to provide an open container.
The container must be made of two sections, depending on local conditions, in the form of an embankment or excavation without a waterproof base.
Direct three volumes of the circuit during the initial water flushing of the equipment into one section, which is smaller in volume and serves to settle corrosion products and mechanical impurities.
The clarified water must be transferred to the second homogenizing section. Effluents from water cleaning of equipment in the amount of 12 circuit volumes when displacing acidic and alkaline solutions should be discharged into the same section.
The capacity of the homogenizer should be selected depending on the type of boiler unit and the volume of the flushed circuit.
The approximate amount of wastewater from pre-start chemical cleaning of equipment is given in table. 4.
Table 4
|
Steam capacity, t/h; boiler type |
Cleaning scheme |
volume of the flushed circuit, m 3 |
Volume of discharged wastewater, m3 |
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into the neutralizer tank |
into the averaging tank |
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420; drum |
Single-circuit |
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640; drum |
Dual-circuit |
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1st circuit |
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|
2nd circuit |
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950; direct-flow |
Single-circuit in two stages |
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|
950; direct-flow |
Dual-circuit |
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|
1st circuit |
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|
2nd circuit |
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|
1600; direct-flow |
Dual-circuit |
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|
1st circuit |
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|
2nd circuit |
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2650; direct-flow |
Double-circuit in two stages: |
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|
1st circuit |
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|
2nd circuit |
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5.7. Water from the stabilizer tank should be used to feed the circulating water supply systems of power plants. For thermal power plants with direct-flow water supply systems and if it is impossible to use this water for own needs, release it into a drainage canal. At the same time, the feasibility of constructing a homogenizing tank is checked.
5.8. The composition of wastewater in mg/l after mutual neutralization in tanks of acidic and alkaline solutions for the chemical treatment methods used is taken according to the table. 5.
Table 5
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Indicators |
Chemical cleaning methods |
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hydrochloric acid |
complexonic |
monoammonium citrate |
Phthalic acid |
NMK concentrate |
dicarboxylic acids |
hydrazine acid |
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Sulfates |
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|
PB-5; IN 1; AT 2 |
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|
Formaldehyde |
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|
Ammonium compounds |
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|
Hydrazine |
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|
Dry residue |
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|
COD mg/l O 2 |
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|
BOD mg/l O 2 |
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* Organic substances are present in the form of salts of organic acids with iron, ammonium, and sodium.
5.9. For final neutralization, precipitation of heavy metal ions (iron, copper, zinc), decomposition of hydrazine, ammonium compounds and other operations, a tank with a conical bottom with a capacity of up to 500 m 3 is required. The tank is equipped with recirculation pumps, air distribution and reagent supply.
Precipitation of iron should be carried out by alkalization with lime:
up to pH = 10 - with hydrochloric acid and hydrazine acid methods;
up to pH = 11 - with the monoammonium citrate method and washing with low molecular weight and dicarboxylic acids and the phthalic acid method;
up to pH = 12 - in the presence of EDTA compounds in solutions.
Settle the wastewater to thicken the sludge and clarify the water for at least two days.
During operational washings to precipitate copper and zinc from monoammonium citrate and complexonate solutions, sodium sulfide should be used, which must be added to the solution after separation of the iron hydroxide sludge.
The sediment of copper and zinc sulfides should be compacted by settling for at least 24 hours.
Sludge, consisting of metal hydroxides and sulfides, is sent to ash and slag dumps and pre-treatment sludge dumps.
Clarified water must be acidified to neutral with pH = 6.5 - 8.5 and disposed of together with other saline wastewater from the power plant in accordance with clause 6.7.
The possibility of supplying these waters to the domestic sewage system, which includes facilities with complete biological treatment, where they will be further purified from organic compounds, should be considered.
5.10. At power plants operating on gas and oil fuel, additional processing and neutralization of neutralized chemical treatment waters can be carried out using a RVP washing water neutralization unit and convective heating surfaces. However, mixing chemical treatment waters and RVP washing waters is unacceptable.
5.11. Neutralizer tanks and wastewater treatment tanks, as well as pipelines within these units, should be protected with anti-corrosion coatings designed to receive wastewater at temperatures up to 100 °C. Pumps for pumping and recycling chemical wastewater must be acid-resistant.
5.12. The quality of clarified water after wastewater treatment must be in accordance with the chemical washing method used.
The average composition of clarified water after wastewater treatment in mg/l is taken according to the table. 6.
Table 6
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Indicators |
Chemical wash methods |
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|
hydrochloric acid |
complexonic |
monoammonium citrate |
phthalic acid |
NMK concentrate |
dicarboxylic acids |
hydrazine acid |
|
|
Sulfates |
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|
PB-5; IN 1; AT 2 |
|||||||
|
Formaldehyde |
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|
Ammonium compounds |
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|
Dry residue |
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|
COD mg/l O 2 |
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|
BOD mg/l O 2 |
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5.13. The amount of sludge as a percentage of the total volume of solution in the wastewater treatment tank is calculated by the formula
Where: ? - amount of sediment in % of the total volume of the solution;
M is the value of the dry residue of the solution, g/l;
T - settling time, days.
6 . Waste water from water treatment and condensate treatment plants
6.1. Quantitative and qualitative indicators of waste water are determined in the design of the technological part of water treatment and condensate treatment.
6.2. Clarifier purge water can be discharged:
b) to neutralize acidic wastewater (at a pH of blowdown water above 9);
c) directly to the sludge dump when the latter is located near a thermal power plant with the return of clarified water from the sludge dump to the tanks for reusing the wash water of mechanical filters;
d) into periodic settling tanks, from which clarified water is returned to the tanks for reusing the washing water of mechanical filters, and the sludge is discharged with neutralized regeneration water of ion exchange filters to a sludge dump;
e) into special devices for sludge dewatering with the return of clarified water to tanks for reuse of flush water from mechanical filters.
The return of clarified water according to points “c”, “d” and “e” should be taken in the amount of 75% of the clarifier purge water consumption.
6.3. Lime waste can be discharged:
a) into the hydraulic ash removal system;
b) to the sludge dump.
6.4. The estimated volume of the sludge dump is accepted for 10 years of operation of the thermal power plant with its designed capacity. The moisture content of the sludge at the sludge dump is assumed to be 80 - 90%.
6.5. In the presence of clarifiers, water from washing mechanical filters of chemical water treatment is collected in a special container (regeneration tank) and, without settling, is pumped evenly throughout the day into the source water line at water treatment plants with coagulation (without liming) or to the lower part of each clarifier for liming the water.
It must be ensured that there are no foreign contaminants in the returned water, no air leaks during pumping, and constant flow.
6.6. In the absence of clarifiers for water coagulation (direct-flow water treatment), water from washing mechanical filters can be sent:
a) into the hydraulic ash removal system;
b) into the system for collecting regeneration water from ion exchange filters;
c) into a special settling tank with return of clarified water to the original water and pumping of sludge to a sludge dump. The feasibility of this should be confirmed by comparison with the option of installing clarifiers instead of direct-flow coagulation.
6.7. Regeneration waters of ion exchange filters, purge waters of evaporators and steam converters, depending on local conditions, can be sent to:
a) into the hydraulic ash removal system using them for the needs of hydraulic transport of ash and slag;
b) into reservoirs, in compliance with sanitary, hygienic and fishery requirements for the water quality of the reservoir at the design site.
With a direct-flow cooling system of thermal power plants, to ensure better conditions for mixing regeneration waters in the reservoir, they are discharged into outlet channels;
c) into evaporation ponds under favorable climatic conditions;
d) for evaporation plants during a feasibility study.
The issue of the necessary neutralization of acidic and alkaline regeneration waters before their discharge must be resolved in each individual case, taking into account local conditions.
Neutralization of acidic and alkaline wastewater is carried out in tanks that have an anti-corrosion coating and are equipped with a supply of air and reagents.
The capacity of the tanks must ensure the reception of regeneration water from the filter unit or daily flow in a parallel circuit, as well as reagents for their neutralization.
In order to reduce the volume of discharged water, in each specific case the issue of using part of the washing water of ion exchange filters (the last part) in the technical water supply or chemical water treatment system must be considered.
6.8. Wash water from electromagnetic filters containing high concentrations of iron oxides in suspension should be directed to ash or sludge dumps.
6.9. The choice of water discharge methods should be made on the basis of technical and economic calculations, taking into account local conditions and standards for the protection of water sources from pollution.
7 . Waters containing “Ivviol” and OMTI
7.1. Due to the lack of methods for treating wastewater from Ivviol and OMTI, devices should be provided for collecting and supplying this water and contaminated sediments to fuel oil tanks with subsequent combustion in boilers.
8 . Wastewater contaminated with petroleum products
8.1. Sources of wastewater contamination with oils can be:
in the main building: oil systems of turbines, generators, exciters, feed pumps, mills, smoke exhausters, fans, oil purification units, pump seal drains, oil spills during repair of oil systems and equipment, drainage water from floors;
in auxiliary rooms of power plants: drains, seals of oil seals of pumps, compressors, fans, floor drains of rooms where there may be leaks and oil spills;
at installation sites for transformers and oil switches: emergency oil drains and drainage of channels and tunnels with oil-filled cables;
in oil production: drainage of oil pump floors, rain and melt water from the open oil storage area;
garages and parking areas for vehicles, tractors, bulldozers, construction machines and other vehicles and mechanisms.
8.2. Sources of wastewater pollution with fuel oil can be:
drains from oil pump seal seals and from condensate control samplers;
drainage water from fuel oil pump floors, fuel oil pipeline channels;
condensate from fuel oil heaters and drain trays;
rain and melt water from the drainage device, the bunded area of the fuel oil warehouse and areas of the fuel oil farm adjacent to the drainage device and the fuel oil pumping station, contaminated during operation;
groundwater intercepted drainage system fuel oil economy, due to the seepage of fuel oil into the ground through leaks in storage tanks and drain trays;
washing waters of condensate purification filters of fuel oil facilities.
8.3. When designing, it is necessary to provide for measures to reduce wastewater pollution with petroleum products, as well as their quantity by:
separation of flows of clean and oil-contaminated wastewater from mechanisms and installations whose rotating units are cooled by water. Cooling water that is not contaminated during operation must have independent discharge pipelines and be returned for reuse;
installation of protective covers on oil and fuel oil pipelines with drainage pipelines to drain oil and fuel oil in case of leaks, breakthrough of flange joint gaskets or desealing of valve seals;
devices for wrapping and pallets in places where oil pumps and oil tanks are installed;
installation of tanks for collecting oil from pallets and from protective casings and tanks for collecting fuel oil from casings of fuel oil pipelines;
wrapping areas for equipment repair and inspection of transformers with local collection and removal of oil;
the use of special devices that prevent splashing and spillage of fuel oil when draining from tanks;
devices on the drainage device of the wrapping at a distance of 5 m from the axis of the railway track and transverse slopes towards the drain trays;
preventing fuel oil from entering the condensate of heaters, monitoring the quality of condensate in each group of heaters with the installation of samplers, alarms for condensate contamination with fuel oil or other devices;
supplying wastewater contaminated with fuel oil from the drainage pits of the fuel oil pump into tanks with fuel oil;
supplying watered fuel oil for combustion in boilers without removing the water contained in it;
preventing the filtration of fuel oil into the ground from tanks and drain trays;
wrappings of equipment repair sites, as well as areas of the fuel oil facility that are contaminated with fuel oil during operation.
8.4. For the collection and subsequent disposal of wastewater contaminated with petroleum products, it is necessary to provide an independent system that must be drained: drains from pump crankcases and rotating mechanisms that do not have separate oil and water drains; rain and melt water from open storages of oil, fuel oil, diesel fuel; from areas of the territory contaminated during operation; from a network of emergency oil drains; drainage water from the floors of the main building, compressor room, workshops and other premises, the floors of which may be contaminated with petroleum products; condensate, with a fuel oil content of more than 10 mg/l and wash water from condensate purification filters.
8.5. The amount of wastewater contaminated with oils should be taken as follows:
constant discharge from the mechanisms and installations of the main building - 5 m 3 / h per unit (turbine-boiler);
constant discharge from all auxiliary premises (compressor rooms, workshops, pumping stations, etc.) - 5 m 3 /h;
periodic discharge from flushing premises floors - 5 m 3 /h.
Periodic discharge of rain and melt water from the territory of an open oil warehouse, open installation of transformers, oil switches, etc. is determined in specific conditions depending on the area and climatic factors.
8.6. The amount of wastewater contaminated with fuel oil should be:
constant consumption depending on the steam output of installed boilers (Table 7);
Table 7
periodic expenses: condensate contaminated with fuel oil more than 10 mg/l, rain and melt water from the embanked territory of the fuel warehouse and from areas of the fuel oil farm that are polluted during operation, wash water from condensate purification filters, discharged, as a rule, through a stabilizer tank.
8.7. The estimated flow rate of wastewater contaminated with petroleum products is determined by summing the constant flows and the largest periodic flow.
When determining the amount of oil-contaminated condensate, the flow rate from the group of heaters with the highest productivity is taken as the calculated one.
8.8. The average content of petroleum products in the total wastewater flow, taking into account the measures set out in paragraph 8.3, should be taken equal to 100 mg/l.
8.9. At power plants operating on solid fuels, wastewater contaminated with petroleum products, as a rule, without treatment, must be reused for the needs of hydroash and slag removal: for flushing and hydraulic transport of ash and slag, for irrigation of wet ash collectors, etc.
The need to treat wastewater from oil products for these power plants must be justified.
8.10. At power plants operating on liquid fuel and gas, treatment of wastewater contaminated with petroleum products must be provided. It is necessary to consider the possibility and feasibility of using existing or planned treatment facilities of neighboring industrial enterprises or populated areas.
It is allowed to supply wastewater contaminated with petroleum products into the sanitary and fecal sewage system, which includes complete biological treatment facilities. The content of petroleum products in the total wastewater flow entering for treatment should not exceed 25 mg/l.
8.11. Design wastewater treatment from oil products according to the following scheme: receiving tank, oil trap, mechanical filters.
The installation of activated carbon filters after mechanical filters must be justified.
Note. It is allowed, according to the conditions of the layout of treatment facilities, to design a pressure flotation unit instead of an oil trap.
8.12. The capacity of the receiving tank should be selected based on the two-hour influx of the estimated flow rate of wastewater and wash water from the filters of treatment facilities.
The receiving tank must be equipped with devices for catching floating oil products and sediment, their removal, as well as for uniform supply of water to the subsequent purification stage.
The residual content of petroleum products after receiving tanks should be 80 - 70 mg/l.
8.13. The design of oil traps (pressure flotation units) should be carried out in accordance with SNiP II-32-74 “Sewerage. External networks and structures" and SN 173-61 "Guidelines for the design of external sewerage for industrial enterprises" Part 1.
The residual content of petroleum products after oil traps (flotation units) should be 30 - 20 mg/l.
8.14. Oil products caught in receiving tanks and oil traps (floaters) must be fed into the fuel oil supply tanks of the power plant for subsequent combustion in boilers. The sludge from these structures is stored in a sludge dump with a waterproof base, with subsequent (after drying) removal to places approved by the State Sanitary Inspectorate. The capacity of the sludge dump is based on the accumulation of sediment in it for 5 years.
8.15. Design mechanical filters with a two-layer loading of quartz sand and crushed anthracite (coke).
The filtration speed should be 7 m/h.
The residual content of petroleum products after mechanical filters should be 10 - 5 mg/l.
8.16. The filtration speed for filters with activated carbon is 7 m/h. The final content of petroleum products in purified waters after carbon filters is up to 1 mg/l.
8.17. Rinsing mechanical and carbon filters should be done with hot water at a temperature of 80 - 90 °C.
The estimated washing speed is 15 m/h.
8.18. Purified water must be reused for the technological needs of the power plant: to feed the circulating technical water supply system or to feed water treatment.
When using water purified from oil products in a circulating technical water supply system, as well as for feeding water treatment plants that have pre-treatment with liming, filters with activated carbon should not be provided as part of treatment facilities.
9 . Wastewater from hydraulic cleaning of fuel supply tract premises
9.1. Hydraulic cleaning systems for fuel supply path premises must be designed to be recirculating without discharging fuel-contaminated water into water bodies.
9.2. To wash away spills, fuel deposits and dust in the premises of the fuel supply path, clarified water from the circulating ash and slag removal system of thermal power plants should be used.
9.3. The discharge of fuel-contaminated water from the hydraulic removal system should, as a rule, be carried out into the channels of the hydraulic ash removal system.
9.4. During a feasibility study, it is possible to design a local recirculating system for hydraulic cleaning of the fuel supply path with facilities for clarification of contaminated water and its return for hydraulic cleaning needs. Replenishment of water losses from this circulating system is carried out with clarified water from hydraulic ash removal or process water.
10 . Rainwater from the power plant area
10.1. The discharge of rain and melt water, as well as industrial wastewater containing petroleum products and chemically harmful compounds, into the rainwater drainage network of power plants must be excluded.
10.2. Areas of the territory of power plants that may be contaminated with petroleum products during operation must have lining, and the drainage of rain and melt water from them should be designed into a wastewater system contaminated with petroleum products.
10.3. The release of rainwater into reservoirs must be designed in accordance with the “Rules for the protection of surface waters from pollution by wastewater.”
The need to treat wastewater discharged by storm drains is determined in the specific conditions of the designed power plant.
10.4. It is necessary to consider the possibility and feasibility of using rain and melt water from the territory of the power plant for our own needs: for feeding circulating water supply systems, feeding water treatment plants, etc.
10.5. Rain and melt water from the roof of the main building, as a rule, must be diverted through a network of internal drains to the technical water supply system, from the roof of the combined auxiliary building - for its own water treatment needs, preparation of reagents, etc.
Application
Calculation of the purging value of the GZU system (calculation method developed by VTI named after F.E. Dzerzhinsky)
Content of sulfates in water added to the gas treatment system, mEq/l;
Q add.in - the amount of water added to the GZU system, m 3 /h;
l- the base of natural logarithms;
Residence time of clarified water in the ash and slag dump basin.
If the value of Qpr, determined from the above equations, turns out to be less than 0.5% of the water flow in the system, the organization of purging can be abandoned.
Thermal power engineering is an industry that makes a significant contribution to environmental pollution. The degree of harm of wastewater from thermal power plants to the environment depends on many factors, the main one of which is the chemical composition of the discharged wastewater. Discharges containing oil and petroleum products, and heavy metals. These pollutants are subject to stringent standards for residual concentrations, which requires serious consideration of industrial wastewater treatment technologies.
The introduction of modern and improved water treatment technologies simultaneously solves the following problems:
- Implementation of processes for softening, deferrization and purification of industrial condensate.
- Cleaning of used cleaning and washing solutions containing caustic and concentrated compounds (acids, alkalis), including solutions for washing steam boilers.
- Purification of oily industrial waters subject to discharge.
- Purification and separation of sludge and oils from storm and melt water collected from the territory of the enterprise.
The step-by-step technology for wastewater treatment at thermal power plants includes the following processes:
- Mechanical cleaning for removing large particles, floating and easily settling suspensions from water.
- Stage physical and chemical cleaning- serves to remove partially dissolved, emulsified and suspended pollutants in the water volume.
- Deep cleaning (additional purification). The degree of effectiveness of this stage of treatment depends on the sanitary and hygienic requirements for wastewater and the category of the reservoir into which the treated water is discharged. Requirements for circulating water purification are determined by technology.
As can be judged from practical experience, at present, thermal power plants mostly use traditional methods for wastewater treatment, which do not allow achieving high degree purity of wastewater. Treatment facilities operate on the principles of mechanical and chemical treatment, and new effective methods are almost never implemented due to the high costs of modernizing and re-equipping treatment facilities.
Factors that negatively affect wastewater treatment processes include:
- long service life of treatment facilities;
- physical and moral aging of equipment, accumulation of equipment wear and tear;
- ineffective, outdated cleaning technologies;
- violations of the operating regime of water treatment complexes;
- heavy loads on treatment facilities, exceeding their design indicators;
- underfunding and untimely repair work;
- shortage and low qualifications of service personnel.
One of the unpleasant consequences of inefficient operation of industrial water treatment is exceeding the permissible load on urban biological treatment systems. Solving these related problems requires new technologies, construction or deep modernization of existing treatment facilities.
New water treatment systems must be designed according to the principle of modularity. Modular treatment systems will allow you to create a treatment complex that will best suit the wastewater parameters (flow rate, chemical composition, degree of contamination) and meet the requirements for treated wastewater at the point of discharge.
Argel
Contaminated wastewater from thermal power plants and their water treatment plants consists of streams of different quantity and quality. They include (in descending order of quantity):
a) wastewater from both circulating and direct-flow (open) hydroash and slag removal systems (HSU) of power plants operating on solid fuels;
b) blowdown water from circulating water supply systems of thermal power plants, discharged continuously;
c) wastewater from water treatment plants (WTP) and condensate treatment plants (CPU), discharged periodically, including: fresh, sludge-contaminated, saline, acidic, alkaline, oily and oil-contaminated waters of the main building, fuel oil and transformer facilities of thermal power plants;
d) blowdown water from steam boilers, evaporators and steam converters, discharged continuously;
e) oily and slushy snow and rain runoff from the territory of the thermal power plant;
f) washing water from RAH and heating surfaces of boilers (wastewater from RAH boilers operating on fuel oil is discharged 1-2 times a month or less, and from other surfaces and when burning solid fuels - more often);
g) oily, contaminated external condensates, suitable after their cleaning for feeding steam evaporator boilers;
h) waste, spent, concentrated, washing acidic and alkaline solutions and wash water after chemical washing and conservation of steam boilers, condensers, heaters and other equipment (discharged several times a year, usually in summer);
i) water after hydraulic cleaning of fuel shops and other premises of thermal power plants (usually discharged once a day per shift, more often during the day).
Relationship between fresh and waste water from power plants
At thermal power plants there must be a unified water supply and drainage system, in which waste water of the same type, directly or after some treatment, could be the source for other consumers of the same thermal power plant (or external ones). For example, waste waters of direct-flow water supply systems after condensers, as well as blowdown waters of circulating systems with a small (1.3-1.5 times) evaporation, as well as oil-contaminated wastewater from thermal power plants can be the source water of the water treatment plant, as well as the last portions washing water from desalting filters.
All waste water returned to the “head” of the process should not need to be treated with reagents during pre-treatment; if it is necessary to treat with lime, soda and coagulant, they should be mixed (averaged) in a collecting tank. The capacity of this tank should be designed to collect 50% of all wastewater from the water treatment unit per day, including 30% of the wastewater from the ion exchange part. It is not advisable to mix clear soft and sludge waste water. It should be taken into account that at least 50% of all waste water of the water treatment plant, including all waste water of pre-treatment of all types, including waste water after loosening ion exchange filters with fresh water, the last portions of washing water of ion exchange filters of desalting plants, as well as water discharged when emptying clarification plants and ion exchange filters, have salt content, hardness, alkalinity and other indicators that are the same or even better than pre-purified and, especially, source water, and therefore can be returned to the “head” of the process, to clarifiers, or, even better, without additional treatment with reagents. for clarification, H- or Na-cation exchange filters.
In addition to a single common sewerage system for all types of fresh water, there must also be separate discharge channels for saline and acidic waters (alkaline waters must be completely used in the cycle, including for neutralization). This water must be collected in special pit tanks.
Due to the periodic operation of earth pits (mainly in the summer) for cleaning solutions and boiler wash waters after chemical washes, after installations for neutralizing these waters and wash waters, the RVP should provide the possibility of supplying various discharged acidic, alkaline and saline waters of the WPU to these structures for joint or alternate neutralization, settling, oxidation and transferring them to the gas storage system or other consumers. When obtaining vanadium oxide from RVP wash waters, these waters are not mixed with others before the vanadium is separated. In this case, the neutralized installation or, at least, its pumps and fittings must be located in an insulated room.
Saline waters after Na-cation exchange filters are divided into three parts according to their quality and used in different ways.
A concentrated spent salt solution containing 60-80% of removed hardness with a 50-100% excess of salt and constituting 20-30% of the total volume of saline water should be sent to the gas treatment system or for softening with return to the water treatment plant, or for evaporation to obtain solid salts Ca, Mg, Na, CI, S0 4, or into earthen pits, from where, after mixing with other wastewater, dilution and joint neutralization, it can be sent to the sewer system, for the needs of thermal power plants or external consumers. The second part of the spent solution, containing 20-30% of the total hardness removed with a 200-1000% excess of salt, should be collected in a tank for reuse. The third and last part - washing water - is collected in another tank for use during loosening, if it cannot yet be sent to the “head” of the process or for the first stage of washing.
Concentrated saline water after Na-cation exchange filters and neutralized water from N-cation exchange and anion exchange filters (the first portions) can be supplied to gas treatment systems for transporting ash and slag. The accumulation of gas compounds Ca(OH) 2 and CaS0 4 in water leads to saturation and supersaturation of water with these compounds, releasing them in solid form on the walls of pipes and equipment. Oils and petroleum products from wastewater remaining in it after oil traps are sorbed by ash and slag when discharged into the gas treatment system. However, with a high content of petroleum products, they may not be completely sorbed and may be present in ash dumps in the form of floating films. To prevent them from entering with the discharged water into public water bodies, receiving wells for discharge water with gates (“pans”) are built at ash dumps to retain floating oil products.
Soft alkaline, sometimes hot, blowdown waters of steam boilers, evaporators, steam converters after using their vapor and heat, as well as soft alkaline washout waters of anion exchange filters can serve as feed water for less demanding steam boilers, and also (in the absence of heat exchangers with brass pipes in the heating system) make-up water for closed heating systems. If they contain Na 3 P0 4 phosphates in an amount of more than 50% of the total salt content, they can be used for stabilization treatment of circulating water, as well as for dissolving salt in order to soften its solution with alkalis and phosphates contained in the blowing water.
When choosing a method for treating saline, acidic or alkaline waters after regeneration of ion exchange filters, sharp fluctuations in the concentrations of soluble substances in these waters should be taken into account: maximum concentrations in the first 10-20% of the total volume of discharged water (the actual waste solutions) and minimum concentrations in the last 60-80 % (washing water). The same concentration fluctuations are observed in waste solutions and wash waters after chemical washes of steam and hot water boilers and other apparatus.
While wash waters with a small concentration of soluble substances can be relatively easily neutralized (mutually), oxidized and generally purified from removable contaminants, purification of a large volume of a more concentrated mixture of waste solutions and wash waters requires large amounts of equipment, significant labor costs, funds and time.
Spent alkaline solutions and wash waters after regeneration of anion exchange filters (except for the first portion of solution after 1st degree filters) must be reused inside the water supply unit. The first portion is sent to neutralize acidic waste waters of water treatment plants and thermal power plants.
Scheme of a drainless thermal power plant
In Fig. 13.18 shows as an example a drainless water supply scheme for a coal-fired thermal power plant. Ash and slag from the boilers are supplied to ash dump 1. Clarified water 2 from the ash dump is returned to the boilers. If necessary, part of this water is purified at a local treatment plant 3. The resulting solid waste 4 is supplied to the ash dump 1. Partially dehydrated ash and slag are disposed of. Dry ash removal is also possible, which simplifies the disposal of ash and slag.
Flue gases from 5 boilers are purified in gas desulfurization unit 6. The resulting wastewater is purified using technology using reagents (lime, polyelectrolytes). Purified water is returned to the gas purification system, and the resulting gypsum sludge is transported for processing.
Wastewater 7 generated during chemical washing, preservation of equipment and washing of convective heating surfaces of boilers is supplied to the appropriate treatment units 8, where it is processed using reagents using one of the previously described technologies. The main part of purified water 9 is reused. Vanadium containing sludge 10 is transported for disposal. Sludge 11 formed during wastewater treatment, together with part of the water, is supplied to the ash dump 1 or stored in special sludge storage tanks. At the same time, as the operating experience of Saransk CHPP-2 has shown, when boilers are fed with distillate distillate, operational cleaning of the boilers is practically not necessary. Consequently, wastewater of this type will be practically absent or its amount will be insignificant. Water from equipment conservation is disposed of in a similar way, or conservation methods are used that are not accompanied by the generation of wastewater. After neutralization, part of this wastewater can be uniformly supplied to the water treatment facility for processing together with the purge waters of the 12 SOO (recirculation cooling system).
The source water is supplied directly or after appropriate treatment at the water treatment plant to the SOO. The need for treatment and its type depend on the specific operating conditions of the thermal power plant, including the composition of the source water, the required degree of its evaporation in the coolant, the type of cooling tower, etc. In order to reduce water losses in the cooler, cooling towers can be equipped with drop eliminators or semi-dry or dry cooling towers can be used . Auxiliary equipment 13, the cooling of which may contaminate the circulating water with petroleum products and oils, is separated into an independent system. The water of this system is subjected to local purification from petroleum products and oil in node 14 and is cooled in heat exchangers 15 by water 16 from the main COO cooling circuit of the turbine condensers. Part of this water 17 is used to replenish losses in the cooling circuit of auxiliary equipment 13. Oil and petroleum products 18 separated in unit 14 are fed into boilers for combustion.
Part of the water 12, heated in the heat exchangers 15, is sent to the VPU, and its excess 19 is sent for cooling in the cooling tower.
Blowing water 12 SOO is processed at a water treatment facility using technology using reagents. Part of the softened water 20 is supplied to make up the closed heating network in front of the heating water heaters 21 of the network water. If necessary, part of the softened water can be returned to the SOO. The required amount of softened water 22 is sent to the MIU. Blowdowns from 23 boilers are also supplied here, as well as condensate 24 from the fuel oil facility directly or after cleaning in unit 25. Oil products 18 separated from the condensate are burned in boilers.
Steam 26 of the first stage of the MIU is supplied to production and to the fuel oil facility, and the resulting distillate 27 is supplied to feed the boilers. Condensate from production and condensate from network heaters 21 after treatment in a condensate treatment unit (CP) are also supplied here. Wastewater from 28 KO and the block desalting plant BOU is used in the water treatment plant. Blowing water 29 MIU is also supplied here to prepare the regeneration solution according to the previously described technology.
Stormwater from the territory of the thermal power plant is collected in the stormwater storage tank 30 and, after local treatment at node 31, is also supplied to the SOO or to the water treatment facility. Oil and oil products 18 separated from water are burned in boilers. Groundwater can also be supplied to the SWS without or after appropriate treatment.
When working using the described technology, lime and gypsum sludge will be formed in significant quantities.
There are two promising directions for creating drainless thermal power plants:
Development and implementation of economical and environmentally advanced innovative technologies for the preparation of additional water for steam generators and make-up water for heating networks;
Development and implementation of innovative nanotechnologies for the most complete processing and disposal of generated wastewater with the production and reuse of initial chemical reagents in the station cycle.
Figure 13. Scheme of thermal power plants with high environmental performance
Abroad (especially in the USA), due to the fact that a license to operate a power plant is often issued under the condition of complete drainage, water treatment and wastewater treatment schemes are interconnected and represent a combination of membrane methods, ion-exchange and thermal desalination. For example, the water treatment technology at the North Lake power plant (Texas, USA) includes two parallel operating systems: coagulation with ferrous sulfate, multilayer filtration, then reverse osmosis, double ion exchange, mixed layer ion exchange or electrodialysis, double ion exchange, ion exchange in a mixed layer.
Water treatment at the Braidwood nuclear station (Illinois, USA) involves coagulation in the presence of a chlorinating agent, lime milk and flocculant, filtration on sand or active carbon filters, ultrafiltration, electrodialysis, reverse osmosis, cation exchange layer, anion exchange layer, mixed layer.
An analysis of the technologies implemented for the processing of highly mineralized wastewater at domestic power plants allows us to assert that complete recycling is feasible only through evaporation in various types of evaporation plants. At the same time, clarifier sludge (mainly calcium carbonate), gypsum-based sludge (mainly calcium sulfate dihydrate), sodium chloride, sodium sulfate are obtained as products suitable for further sale.
At the Kazan CHPP-3, a closed cycle of water consumption was created through the complex processing of highly mineralized wastewater from the thermal desalting complex to produce a regeneration solution and gypsum in the form of a commercial product. When operating according to this scheme, an excess amount of evaporation unit purge water is formed in a volume of about 1 m³/h. The purge is a concentrated solution that mainly contains sodium cations and sulfate ions.
Figure 14. Technology for processing wastewater from the thermal desalting complex of Kazan CHPP-3.
1, 4 – clarifiers; 2, 5 – clarified water tanks; 3, 6 – mechanical filters; 7 – sodium cation exchange filters; 8 – tank, chemically purified water; 9 – chemically purified water to make up the heating network; 10 – concentrate tank of the evaporation unit; 11 – reactor tank; 12, 13 – tanks for various purposes; 14 – tank of clarified solution for regeneration (after acidification and filtration) of sodium cation exchange filters; 15 – crystallizer; 16 – crystallizer-neutralizer; 17 – thermochemical softener; 19 – bunker; 20 – pit; 21 – excess evaporator purge; 22 – filter with active carbon loading; 23 – electric membrane unit (EMU).
An innovative nanotechnology has been developed for processing excess purge water of a thermal desalting complex based on an electric membrane installation to produce alkali and softened water. The essence of the electromembrane method is the directed transfer of dissociated ions (salts dissolved in water) under the influence of an electric field through selectively permeable ion-exchange membranes.