Code for design of indirect dry cooling system for fossil-fired power plant
DL/T 5545-2018
Explanation of provisions
Formulation instructions
DL/T 5545-2018 Code for design of indirect dry cooling system for fossil-fired power plant was approved and issued by the National Energy Administration with No.8 Notice on June 6, 2018.
The formulation of this Code mainly followed the following principles:
1 According to China's national conditions, the indirect dry cooling system is designed to meet the requirements of safety, reliability, advanced technology, environmental protection, resource conservation and economic applicability;
2 Unify the definitions of related terms and related calculation methods of indirect dry cooling system of fossil-fired power plants;
3 Put forward the basic requirements for the overall performance and functions of each subsystem of indirect dry cooling system of fossil-fired power plant;
4 Vigorously implement the national policy of energy conservation, resource conservation and environmental protection.
This Code is a newly compiled code. The drafting group investigated the design, test, operation and maintenance conditions of indirect dry cooling system of fossil-fired power plants in Shaanxi, Shanxi, Ningxia and Xinjiang in recent years, with 10 power plant projects in total, of which 4 adopt indirect dry cooling tower with flue gas discharge with built-in desulfurization device, 2 adopt indirect dry cooling system with jet condenser, 4 in the mode with two units sharing one natural draught indirect dry cooling tower, and 1 adopts mechanical draught indirect dry cooling tower. Investigation report of indirect dry cooling power plant, Research report on selection of cooling capacity design margin of indirect dry cooling system, Summary report on performance test of indirect dry cooling tower, Special research report on configuration of indirect dry cooling tower and Special research report on minimum control distance between indirect dry cooling tower and other buildings were compiled.
For the purpose of relevant personnel of design, construction, operation and management having a profound understanding and correct implementation of this Code, the drafting group compiles the provision explanations in sequence of clause, subclause and article, explaining the purpose and reference of the provisions as well as the matters to be concerned in implementation. However, instead of sharing equivalent force of law with the code text, this explanation only serves as the reference for the users to understand and grasp those specified in this Code.
Content
1 General provisions 66
3 Basic requirements 66
4 Meteorological parameter selection requirements of indirect dry cooling system 70
5 General layout of indirect dry cooling system 72
6 Design parameter selection and calculation of indirect dry cooling system 91
6.1 General requirements 91
6.2 Design parameter selection of indirect dry cooling system 92
6.3 Calculation of indirect dry cooling system 94
6.4 Design margin of indirect dry cooling system 99
7 Indirect dry cooling process system and equipment 102
7.1 Indirect dry cooling radiator system 102
7.2 Steam condenser 107
7.3 Circulating water pump and piping system 109
7.4 Expansion water tank system 112
7.5 Underground water storage tank and water filling and drainage system 113
7.6 Radiator cleaning system 115
7.7 Water quality control of circulating water system 116
7.9 Testing and instrumentation, alarm 116
7.10 Insulation, painting and heat tracing 117
8 Indirect dry cooling tower structure 117
8.1 General requirements 117
8.2 Main structure of indirect dry cooling tower 120
8.3 Widening platform 123
8.4 Tower core structure of horizontal radiator arrangement 124
8.5 Accessory structure 125
9 Operation and control requirements of indirect dry cooling system 127
9.2 Normal operation 127
9.3 Winter operation 127
9.4 Summer operation 128
10 Test requirements of indirect dry cooling system 129
10.1 Mathematical and physical model test of indirect dry cooling system 129
10.2 Performance test of indirect dry cooling system 130
1 General provisions
1.0.2 The indirect dry cooling system of fossil-fired power plant refers to the exhaust steam cooling system of steam turbine used for driving main engine and auxiliary engine, in which there is steam condenser. If the auxiliary engine equipment adopts dry cooling radiator with mechanical draught cooling tower for cooling, it is generally called auxiliary engine dry cooling system, which is not an indirect dry cooling system.
3 Basic requirements
3.0.1 The types of dry cooling system mainly include direct dry cooling system and indirect dry cooling system. According to the draught mode, it may be divided into natural draught type and mechanical draught type. It is necessary to reasonably determine the type of dry cooling system through technical and economic comparison according to factors such as construction conditions, meteorological conditions, anti-noise requirements, land occupation of cooling facilities, freeze resistance and performance for passing summer, and unit operation requirements.
The types of dry cooling systems widely used in China mainly include mechanical draught direct dry cooling system and natural draught indirect dry cooling system.
The characteristics of mechanical draught direct dry cooling system are as follows: the anti-freezing performance is relatively good in winter, and it has run performance in extremely cold areas in China, which is suitable for the anti-freezing requirements of steam turbine exhaust volume reduction in thermal power plants in winter; the land occupation of the plant is small; the number of axial flow fan units is large, which is beneficial to adjustment; the cooling equipment is made of steel materials, and the condensate system operates under alkaline or neutral water conditions. However, it is sensitive to environmental meteorological conditions, especially in summer, affected by wind velocity, wind direction and strong convective climate change; the vacuum volume is large and the vacuum tightness is high, which affects the quality of condensed water; the noise of the axial flow fan unit is large; the power consumption rate of the plants under design conditions is relatively high.
The indirect dry cooling system with surface condenser is widely adopted as natural draught indirect dry cooling system in China. Compared with the mechanical draught direct dry cooling system, it has the following characteristics: relatively low sensitivity to environmental meteorological conditions, especially to wind velocity, wind direction and strong convective climate in summer; the vacuum volume is equivalent to the wet cooling system, and the vacuum-pumping system is small in scale; the arrangement of indirect dry cooling tower is relatively flexible; the power consumption rate of the plants under design conditions is relatively low; the noise is low. However, the anti-freeze performance in winter is relatively poor; the land occupation of cooling facilities is large; the engineering investment is relatively high; the construction period of large indirect dry cooling tower is long; the adjustment of air volume using natural draught is limited; if all-aluminum cooling elements are used, the pH value of circulating water shall be controlled.
At present, the design and manufacture of natural draught direct dry cooling system in China are immature. Therefore, due to the limitation of noise requirements, if mechanical draught direct dry cooling system cannot be adopted, only natural draught indirect dry cooling system can be considered.
In view of the characteristics of the above two dry cooling systems, natural draught indirect dry cooling system will be given priority for plant site with disordered flow state of the environmental wind field, high wind velocity, stringent standard requirements for ambient noise and the need for arranging dry cooling tower with flue gas discharge.
Dry cooling units are generally used in water-deficient areas, so it is not recommended to adopt dry cooling and wet cooling system, or set up spray cooling system for dry cooling radiator in summer. Through investigation, most natural draught indirect dry cooling towers in power plants do not have spraying facilities. If spraying facilities are installed in some cases, the operation effect is not ideal, the consumption of desalted water is large, and the operation cost is high, so it is not recommended to set up spray cooling system for dry cooling radiator in summer.
The advantages of mechanical draught indirect dry cooling tower are small land occupation, flexible operation adjustment, favorable anti-freezing, short civil construction period, and the disadvantages are similar to those of mechanical draught direct dry cooling tower, namely, large noise and power consumption of fan groups. Generally, when the cooling water flow rate is small, the natural draught indirect dry cooling tower is limited by the tower type, the wind velocity at windward side is low, and the heat dissipation area is relatively large, so it is more economical to adopt the mechanical draught indirect dry cooling tower.
The heat transfer efficiency of dry cooling tower is far lower than that of wet cooling tower. Even for 300MW dry cooling units, the size of indirect dry cooling tower corresponding to it will reach or exceed that of cooling tower of 600MW wet cooling units. Engineering practice shows that if 300MWh or above condensing dry cooling units adopt mechanical draught dry cooling tower, they also need a large number of indirect dry cooling tower units, which shall be considered according to local conditions in terms of land occupation. Mechanical draught dry cooling towers also have energy consumption of fans, and generally have no advantages in economy. Therefore, it is suggested that 300MWh or above condensing units be equipped with natural draught indirect dry cooling tower. However, when the heat load of heating units varies greatly in winter, it may be far lower than that of pure-condensing units. Some of them using mechanical draught cooling towers may facilitate anti-freezing adjustment, and cooling mode combining natural draught and mechanical draught may be selected according to the heat exhaust and anti-freezing requirements.
3.0.2 Indirect dry cooling system with jet condenser is also called Heller system. For the indirect dry cooling system with jet condenser, the biggest difference of it from indirect dry cooling system with surface condenser is that it adopts the jet mixing condenser through which the cooling water in the system enters the condenser, is jetted, directly mixed with and condenses the exhaust steam of steam turbine; the terminal temperature difference (TTD) between the exhaust steam of the jet mixing condenser and the outlet water of the circulating water of the condenser is small, and the designed calculated value is only 0.5℃~1.0℃, however, due to the influence of the design performance and installation quality of the jet mixing condenser, the terminal temperature difference (TTD)c measured on site under rated load deviates from the TTD to some extent; due to the mixing of circulating water and condensed water, and the circulating water is large in amount and circulates repeatedly through radiators and circulating water pipes, the water quality is more likely to deteriorate, so it is difficult to control the water quality; the head of circulating water pump in indirect dry cooling system with jet condenser includes the pressure difference between atmospheric pressure and condenser pressure, the difference between water surface elevation at the top of radiator and condenser water level elevation, and the total water resistance of circulating water in hot pipe section, the total water resistance of cold water section and the working head of nozzle shall be overcome in the return section, the throttle head may be recovered by hydraulic turbine, due to the influence by the efficiency of hydraulic turbine, generally 25% ~ 30% of energy may be recovered, therefore, under the condition of the same circulating water amount, radiator and circulating water pipe arrangement, the power consumption of circulating water pump in indirect dry cooling system with jet condenser is higher than that of indirect dry cooling system with surface condenser; the indirect dry cooling systems with jet condenser of 200MW, 300MW and 600MW units that have been put into operation in China all adopt imported jet mixing condensers and circulating water pump units with hydraulic turbines, and the design and manufacture of domestic equipment are not mature. In recent years, most of the newly built indirect dry cooling units in China have adopted the indirect dry cooling system with surface condenser.
3.0.3 In 17.8.12 of the current national standard GB 50660-2011 Code for design of fossil fired power plant, it is specified that if the dry cooling unit adopts steam-driven water-feeding pump, the indirect dry cooling system should be adopted as the cooling mode of exhaust steam of water-feeding pump steam turbine. This provision emphasizes that wet cooling system should not be used for the cooling mode of exhaust steam of water-feeding pump steam turbine of dry cooling unit from the perspective of water conservation. Indirect dry cooling systems are seldom used in large- and medium-sized thermal power units over 300MW in China during the compilation and review of this Code. This Code emphasizes that the exhaust steam cooling facilities of water-feeding pump steam turbine of indirect dry cooling units shall be combined with the cooling facilities of main engine and should not be set separately; if the main engine is a unit with direct dry cooling system, independent indirect dry cooling unit may be adopted for cooling the exhaust steam of water-feeding pump steam turbine. In recent years, induced draft fan steam turbines have also been used. The steam turbines for auxiliary engine drive include water-feeding pump steam turbines, induced draft fan steam turbines and other auxiliary engines that may be driven by steam turbines.
3.0.4 In addition to common anti-freezing measures, special anti-freezing measures for indirect dry cooling system are mainly as follows: temporary measures of hanging canvas outside louvers or setting windproof curtains that may be lifted automatically, and increasing the frequency of monitoring the cooling delta water temperature and cooling column wall temperature.
The design measures against strong wind of indirect dry cooling system: firstly, according to the design ambient wind velocity, reasonably determine the scale and margin of dry cooling system; in addition, the strong wind prevention measures that can be used for reference include setting wind guide walls around the indirect dry cooling system and setting wind protection measures in the windward direction of the dominant wind.
The design of anti-floating objects is difficult, which mainly relies on strengthening the design of cleaning system, for example, when conditions permit, arrange cleaning facilities inside and outside the tower at the same time; increase the number of radiators to be cleaned at the same time to speed up the cleaning; realize fully automatic cleaning process to reduce the labor intensity of cleaning.
3.0.5 Among the dry cooling units under construction and put into operation at present, 300MW units adopting the configuration of one unit and one tower and two units and one tower, and units above 600MW adopting the configuration of one unit and one tower have been successfully applied in practice. Considering that for units above 600MW, if two unit are configured with one indirect dry cooling tower, the scale of the dry cooling tower is usually extremely large and the implementation difficulty is greatly increased, so this article is given. However, with the advent of radiators with larger finning coefficient in recent years, engineers and technicians have been studying the possibility of two units and one tower for 600MW units, so the feasibility of two units and one tower for 600MW units cannot be ruled out. This article does not specify the configuration form of indirect dry cooling system of units below 600MW, which may be determined by comprehensive comparison and demonstration of actual engineerings in design.
4 Meteorological parameter selection requirements of indirect dry cooling system
The contents of this clause are stipulated according to the requirements of current professional standards DL/T 5158 Technical code for meteorological survey in electric power engineering and DL/T 5507 Regulation for basic data and depth of the hydraulic design for fossil-fired power plant; specific requirements are put forward according to the characteristics of indirect dry cooling system; the selected reference meteorological station needs to have historical observation data of more than 10 years and self-recorded records of wind velocity, wind direction and air temperature in the last 10 years. When the cooling type of dry cooling system has not been determined, the meteorological parameters of dry cooling system shall meet the design requirements of both direct dry cooling system and indirect dry cooling system.
4.0.2 According to the relevant requirements of the current professional standard DL/T 5158 Technical code for meteorological survey in electric power engineering, the typical year shall be selected according to the following methods:
(1) Calculate the annual average temperature in the last 10 years based on the data of reference meteorological station, then calculate the arithmetic annual average of hourly temperature statistics in each of the last 5 years, and take the year in which the arithmetic annual average is closest to the annual average temperature in the last 10 years as the typical year;
(2) If the arithmetic annual average temperatures in several years are similar to the average temperature in the last 10 years, select the year in which the arithmetic annual average temperature is higher than the average temperature in the last 10 years as the typical year;
(3) If there are still many years in which the arithmetic annual average temperatures are similar to the average temperature in the last 10 years, select the year with higher average temperature and the most uneven distribution in hot season as the typical year.
4.0.3 It is specified in 5.4.1 of current professional standard DL/T 5158-2012 Technical code for meteorological survey in electric power engineering that "The air temperature shall be graded by 0.1℃ in principle", and it is explained in the provision explanation of this article that "Grading adjustment may be carried out in special cases. In order to shorten the length of the grading statistical table, it may generally be graded by 0.5℃." In the actual design of direct dry cooling system and indirect dry cooling system, it is common to grade the air temperature by 0.5℃, 1℃ and 2℃, so this Code stipulates that the air temperature should not be graded by larger than 2℃.
4.0.4 The design wind velocity of indirect dry cooling system is the wind velocity at an elevation of 10m from the ground, so the relevant ambient wind data shall include the wind velocity and wind direction data at an elevation of 10m.
4.0.6 It is specified in 5.1.1 of current professional standard DL/T 5158-2012 Technical code for meteorological survey in electric power engineering that "reference meteorological station shall be selected according to the principle of close natural geographical conditions and similar underlying surface conditions, and distance should not be taken as a single selection criterion". Generally, if one of the following situations occurs in the engineering, the dry cooling meteorological observation station at the plant site will be set up:
(1) The topography and geomorphology change greatly between the plant site and the reference meteorological station;
(2) The buildings, structures and vegetation conditions around the reference meteorological station are quite different from those of the plant site area;
(3) There is a large mountain or valley between the plant site and the reference meteorological station;
(4) When the distance between the plant site and the reference meteorological station is far or the height difference is large.
1 General provisions
3 Basic requirements
4 Meteorological parameter selection requirements of indirect dry cooling system
5 General layout of indirect dry cooling system
6 Design parameter selection and calculation of indirect dry cooling system
6.1 General requirements
6.2 Design parameter selection of indirect dry cooling system
6.3 Calculation of indirect dry cooling system
6.4 Design margin of indirect dry cooling system
7 Indirect dry cooling process system and equipment
7.1 Indirect dry cooling radiator system
7.2 Steam condenser
7.3 Circulating water pump and piping system
7.4 Expansion water tank system
7.5 Underground water storage tank and water filling and drainage system
7.6 Radiator cleaning system
7.7 Water quality control of circulating water system
7.9 Testing and instrumentation, alarm
7.10 Insulation, painting and heat tracing
8 Indirect dry cooling tower structure
8.1 General requirements
8.2 Main structure of indirect dry cooling tower
8.3 Widening platform
8.4 Tower core structure of horizontal radiator arrangement
8.5 Accessory structure
9 Operation and control requirements of indirect dry cooling system
9.2 Normal operation
9.3 Winter operation
9.4 Summer operation
10 Test requirements of indirect dry cooling system
10.1 Mathematical and physical model test of indirect dry cooling system
10.2 Performance test of indirect dry cooling system
