Discharge requirements for cooling seawater
1 Scope
This standard specifies the control requirements, monitoring requirements and result determination methods for discharging cooling seawater.
This standard is applicable to enterprises that discharge cooling seawater to sea areas or estuarine waters (the annual probability for salinity greater than 0.5% is greater than 10%). For seawater cooling construction projects, their environmental impact assessment, environmental protection facilities design and environmental protection acceptance may also refer to this standard.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 12763.2 Specifications for oceanographic survey - Part 2: Marine hydrographic observation
GB/T 12763.4 Specifications for oceanographic survey - Part 4: Survey of chemical parameters in sea water
GB/T 15441 Water quality - Determination of the acute toxicity - Luminescent bacteria test
GB 17378.4 The specification for marine monitoring - Part 4: Seawater analysis
GB 18421 Marine biological quality
GB 18486 Standard for pollution control of sewage marine disposal engineering
GB 18668 Marine sediment quality
GB/T 33584.2 Seawater quality requirements and analysis methods for seawater cooling system - Part 2: Determination of zinc
HJ/T 92 Technical requirements for monitoring of total amount of pollutants in waste water
HJ/T 373 Technical specifications of quality assurance and quality control for monitoring of stationary pollution source (on trial)
HJ 585 Water quality - Determination of free chlorine and total chlorine - Titrimetric method using N,N-diethyl-1,4-phenylenediamine
HJ 586 Water quality - Determination of free chlorine and total chlorine - Spectrophotometric method N,N-diethyl-1,4-phenylenediamine
HY/T 147.1 Code of practice for marine monitoring technology - Part 1: Seawater
HY/T 147.6 Code of practice for marine monitoring technology - Part 6: Marine hydrology, meteorology and sea ice
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
cooling seawater
seawater used as heat exchange medium in the seawater cooling system
Note: It includes seawater from once-through cooling system and seawater from recirculating cooling system.
3.2
seawater from once-through cooling system
seawater in the once-through seawater cooling system, which is directly discharged after a heat exchange in the heat exchange equipment
3.3
seawater from recirculating cooling system
seawater in the recirculating seawater cooling system, which is cooled by a cooling tower and then recycled for use after a heat exchange in the heat exchange equipment
3.4
effluent volume
amount of wastewater discharged outside the legal boundaries of the enterprise from the cooling seawater discharge outlet
Note: It includes the cooling discharge water and various seawater-based wastewater that need to be discharged together with the cooling discharge water.
3.5
benchmark effluent volume per unit product
upper limit of cooling water discharged per unit product
Note: The unit is m3/t or m3/(MW·h).
3.6
initial dilution
number of times the cooling seawater is diluted when the exit momentum and buoyancy actions (under which, the cooling seawater will be mixed with the environmental water body and diluted after it is discharged) are essentially complete
Note: It is revised from Definition 3.4 of GB 18486-2001.
3.7
mixing zone
superimposed (i.e., envelope) area where the concentration of pollutants in nearby waters exceeds the average target limit of water quality in the waters at each instant due to continuous discharge of cooling seawater
Note: It is revised from Definition 3.5 of GB 18486-2001.
4 Control requirements for discharging cooling seawater
4.1 The quality of discharged cooling seawater shall meet those specified in Table 1.
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Table 1 Requirements for quality of discharged cooling seawater
S.N. Water quality index Unit Limit Monitoring position
1 Suspended substance (SS) mg/L ≤30 Cooling seawater discharge outlets of enterprises or shafts on the shore
Man-made increment ≤20 (executed where there is a background value)
2 Water temperature ℃ Man-made seawater temperature rise shall not exceed 9℃ a (10℃ b) in summer and 12℃ a (16℃ b) in winter in terms of the local temperature at that time. Cooling seawater discharge outlets of enterprises or shafts on the shore
Man-made seawater temperature drop shall not exceed 5℃ c in terms of the local temperature at that time.
Man-made seawater temperature rise or temperature drop c shall not exceed 4℃ in summer and 3℃ in winter in terms of the local temperature at that time. Edges of mixing zone
3 pH value - 6.0~9.0, and at the same time, it shall not exceed the normal pH variation range of the water area by 0.5pH Cooling seawater discharge outlets of enterprises or shafts on the shore
4 Chemical oxygen demand (CODMn) mg/L ≤7
mg/L Man-made increment ≤2 (executed where there is a background value)
5 Inorganic nitrogen (counted by N) mg/L ≤1.0
6 Total residual chlorine d mg/L <0.1
7 Total chromium e mg/L ≤0.5
8 Hexavalent chromium e mg/L ≤0.05
9 Copper f mg/L ≤0.1
10 Zinc mg/L ≤0.5
11 Total phosphorus (counted by P) mg/L ≤0.5
Man-made increment ≤0.05 (executed where there is a background value)
12 Petroleum g mg/L <5.0 Cooling seawater discharge outlets of enterprises or shafts on the shore
13 Acute toxicity (HgCl2 toxicity equivalence) mg/L 0.07
Notes: Items listed under numbers 1~3, 6 and 13 are applicable to seawater from once-through cooling system, and Items listed under numbers 1~13 are applicable to seawater from recirculating cooling system.
a It is applicable to thermal power industry and other industries.
b It is applicable to nuclear power units.
c It is applicable to industries that take seawater as the heat source of liquefied natural gas (LNG).
d Test the total residual chlorine when adding chlorine-based biocide.
e Test the content of total chromium and hexavalent chromium when adding chromate corrosion inhibitor.
f Test the content of copper in cooling water system with copper-containing chemicals and/or copper materials.
g It is applicable to oil refining enterprises.
4.2 The benchmark effluent volume per unit product of cooling seawater shall comply with those specified in Table 2.
Table 2 Benchmark effluent volume per unit product of cooling seawater
Industry Cooling mode Limit Position for monitoring pollutant discharge
Thermal power Direct current <120m3/(MW·h) The gauge position of effluent volume is the same as the position for monitoring pollutant discharge
Circulation <3.0m3/(MW·h)
Nuclear power Direct current <230m3/(MW·h)
Circulation <6.0m3/(MW·h)
Others Direct current -
Circulation <3.0m3/t
4.3 The selection of cooling seawater discharge outlet and the design of the effluent discharge system shall make the initial dilution of the cooling discharge water at a time guarantee percentage of 90% in a year meet the requirements of GB 18486.
4.4 The determination of mixing zones for discharging cooling seawater into the sea shall comply with the requirements of GB 18486.
4.5 The cooling seawater should be discharged independently. If it is really necessary to discharge the cooling seawater together with the wastewater from other seawater sources, the latter shall not reduce the discharge quality of the cooling seawater; otherwise, the wastewater from other seawater sources shall be treated.
4.6 The discharge of the cooling seawater shall not cause oil film, floating foam and other floating substances on the surface of the receiving water.
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4.7 The discharge outlet of the cooling seawater should be set offshore, selected in the sea area which is conducive to the transport and diffusion of pollutants to the open sea, and selected by following the principle of keeping away the vortex and wave breaking zones caused by specific terrain such as headland. The discharge outlet should not be close to intertidal zones, and floodplain discharge is prohibited.
4.8 The site selection of the cooling seawater discharge outlets shall not affect the fish migration pathway or the use functions of the adjacent functional areas outside the mixing zone. In the estuary, the lateral width of the mixing zone shall not exceed 1/4 of the width of the estuary.
4.9 The type of the cooling seawater discharge outlet should be determined by comparison and selection to minimize the influence range of the cooling seawater.
4.10 The water quality of the sea area where the discharge outlet is located, the requirements for functional areas, and other surrounding emission sources shall be considered comprehensively in case of calculating the allowable discharge amount of various pollutants in Table 1. For key sea areas where total discharge amount of pollutants is controlled, the indexes for control of total discharge amount of pollutants in this sea area shall be considered in case of determining the allowable discharge amount of pollutants in cooling seawater.
4.11 If two or more different types of seawater-based wastewater with different effluent concentrations are discharged from the same discharge outlet, the effluent concentration of the mixed wastewater shall be calculated in accordance with Annex A.
4.12 The maximum allowable discharge load capacity of water quality indexes of the cooling seawater discharged shall be calculated in accordance with Annex B.
4.13 The maximum allowable total annual discharge amount of water quality indexes of the cooling seawater discharged shall be calculated in accordance with Annex C.
4.14 The cooling seawater shall not cause degradation and change of biological community structure outside the mixing zones of pollutant receiving area.
4.15 The cooling seawater shall not cause toxic substances to be enriched to harmful extent in sediments or organisms in the pollutant receiving area, that is, the quality of sediments in the pollutant receiving area cannot meet the requirements of GB 18668 and the biological quality cannot meet the requirements of GB 18421.
4.16 For cooling seawater, the recycling disposal method should be preferred.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Control requirements for discharging cooling seawater
5 Monitoring requirements
6 Result judgment
Annex A (Normative) Calculation of maximum allowable effluent concentration of pollutants in mixed wastewater
Annex B (Normative) Calculation of maximum allowable discharge load of pollutants in cooling seawater
Annex C (Normative) Calculation of maximum allowable total annual discharge amount of pollutants in cooling seawater
