Common antifreeze and anticondensation methods in power plants include emptying, insulation, heating, circulation and other methods. Winter antifreeze and anticondensation should be carried out according to the operating status of equipment and pipelines, combined with the problems and experience encountered in the antifreeze process in previous years, and one or more of these methods should be adopted.
1. Emptying
The emptying antifreeze and anticondensation methods can be roughly divided into three categories:
The first is the emptying of equipment and pipelines that are intermittently operated or unused for a long time on the ground. The emptying process can be carried out according to the following steps:
(1) Close the relevant valves and add blind plates when necessary to prevent internal leakage of the valves;
(2) Open the high-point exhaust valve and the low-point drain valve to empty the materials in the equipment;
(3) Use nitrogen to purge and replace the remaining materials;
(4) Keep the low-point drain valve open and check regularly.
The second is to empty the facilities and pipelines in the underground valve well. It is mainly fire-fighting facilities without heating (such as water cannons and fire hydrants). Close the root valve from the valve well, drain the water above the valve through the drain valve, and keep the drain valve open with the fire cannon head facing downward.
The third is temporary equipment, pipelines or hoses. After use, the medium in the pipe should be emptied in time and purged with nitrogen; if conditions permit, it can be placed in an insulated plant.
2. Insulation
From the perspective of antifreeze, the insulation of power plants mainly involves the following three aspects:
First, the equipment, pipelines and their accessories are insulated with insulation cotton. Before winter, this work should be carefully checked and improved in combination with the problems that occurred in previous years, especially the insulation of equipment, pipeline ends, blind ends and on-site pressure gauges that are not heated and only rely on material temperature for antifreeze, to ensure that the insulation is in place.
Second, indoor spaces such as factories are sealed and warmed. Check and confirm whether the doors, windows and curtains of the factory are intact, and put the heating in the factory into use in time.
Third, underground valve wells are sealed and warmed. For valve wells, plastic sheets are used to seal in advance, and insulation measures are taken when necessary.
3. Heating
As far as winter antifreeze is concerned, common heating media include hot water heating, steam heating and electric heating. Hot water heating is suitable for conditions where the operating temperature is not high or high-temperature heating media cannot be used. Steam heating is generally used for heating when the operating temperature of the medium in the pipe is less than 150°C.
Electric heating is not only suitable for various situations of steam heating but also for heat-sensitive medium pipelines. It can effectively control the temperature and prevent the pipeline temperature from overheating. It is suitable for heating pipelines or equipment that are dispersed or far away from the gas supply point and equipment with irregular shapes.
The selection of heating media should be based on material properties, index requirements, construction difficulty, operating costs, etc., and construction should be carried out in accordance with specifications to achieve the purpose of antifreeze and anti-condensation while avoiding new problems.
4. Circulation
The method of adopting circulation antifreeze and anti-condensation is mainly used for equipment and pipelines that are intermittently operated or not used for a long time, and the above methods (emptying, insulation, heating) are not adopted for antifreeze, or the above methods cannot meet the antifreeze requirements. This method is roughly divided into four ways:
First, the material at the outlet of the running equipment is refluxed to the inlet of the standby equipment for circulation. This method is often used for standby moving equipment to prevent freezing and condensation, such as bypassing the pipeline through the pump outlet one-way valve, or opening the valve core of the one-way valve.
Second, it is connected to the equipment outlet pipeline through the equipment inlet pipeline. This method is often used to prevent freezing of the inlet and outlet pipelines of the heat exchanger that are not in use. Connect a pipeline with a smaller diameter before the inlet valve of the heat exchanger and after the outlet valve to keep the medium in the inlet and outlet pipelines circulating.
Third, circulate in small quantities according to the normal operating mode. Generally, try to close the outlet valve of the standby equipment as much as possible to reduce the circulation volume of the medium and meet the antifreeze requirements.
Fourth, a small amount of medium is discharged continuously or intermittently. This method is mainly used for antifreeze at the end of the circulation pipeline where it is impossible to establish, such as hose stations, tank dehydration pipelines and valves, steam pipeline low-point drain valves, eyewashers, etc.
