How do chemical plants prevent freezing and conden

How do chemical plants prevent freezing and condensation in winter

how do chemical plants prevent freezing and condensation in winter

December 8th, 2020

the anti freezing and anti condensation work of the chemical plant in winter is the main means to ensure safe production. In order to strictly prevent all freezing accidents, according to the characteristics of the device, the anti freezing and anti condensation work should also be carried out in accordance with the policy of "prevention first, supplemented by elimination". Strengthen the collection, delivery, use and management of items that are easy to freeze and condense, prevent them in advance according to the basic methods, carefully inspect them according to the regulations, and reasonably deal with the problem of freezing and blocking, so as to achieve the purpose of ensuring safe production

I. antifreeze methods

the common antifreeze and anticoagulation methods in chemical plants include emptying, heat preservation, heat tracing, circulation and other methods. In winter, antifreeze and anticoagulation should be coated by one or more methods according to the operating state of equipment and pipelines, combined with the problems and experience in the antifreeze process in previous years

1. Empty. The methods of emptying anti freezing and anti condensation can be roughly divided into three categories:

first, the equipment and pipelines that are operated intermittently on the ground or are not used for a long time can be emptied according to the following steps:

(1) close relevant valves and add blind plates if necessary to prevent valve leakage

(2) open the high point exhaust valve and low point exhaust valve to empty the materials in the equipment

(3) purge and replace residual materials with nitrogen

(4) normally open the low point drain valve and check it regularly

second, the facilities and pipelines in the underground valve well are emptied, mainly the fire-fighting facilities without heat tracing (such as water monitor and fire hydrant). Close the root valve from the valve well, drain the water on the upper part of the valve through the drain valve, keep the drain valve normally open, and the fire monitor head downward

third, the temporarily used equipment, pipelines or hoses should be emptied in time after use, and purged with nitrogen; If possible, it can be placed in the insulation plant

2. Heat preservation. From the perspective of antifreeze, the chemical plant insulation mainly involves the following three aspects:

first, the equipment, pipelines and their accessories should be insulated with insulation cotton. Before winter, the problems in previous years should be combined. This work should be carefully checked and improved, especially the insulation of equipment, pipeline ends, blind ends and on-site pressure gauges that do not have heat tracing and only rely on material temperature for antifreeze, so as to ensure that the insulation is in place

second, indoor spaces such as the plant are sealed and kept warm. Check and confirm whether the doors, windows and curtains of the plant are in good condition, and put the heating in the plant into use in time

third, the underground valve well shall be sealed and kept warm. For the valve well, plastic cloth shall be used to seal it in advance, and insulation measures shall be taken when necessary

3. Heat tracing. In terms of winter antifreeze, common heat tracing media include hot water heat tracing, steam heat tracing and electric heat tracing. Hot water tracing is applicable to the condition that the operating temperature is not high or high-temperature tracing medium cannot be used. Steam heat tracing is generally used for heat tracing when the operating temperature of the medium in the pipe is less than 150 ℃

electric heat tracing is not only suitable for steam heat tracing to avoid various conditions due to impurities such as water, but also suitable for heat sensitive medium pipelines. It can effectively control the temperature and prevent the pipeline temperature from overheating. It is suitable for heat tracing of pipelines or equipment scattered or far away from the gas supply point and equipment with irregular shape

the selection of heat tracing medium should be combined with material properties, index requirements, construction difficulty, operation cost and other aspects, and the construction should be carried out in accordance with the specifications to achieve the purpose of antifreeze and anticoagulation, while avoiding new problems

4, cycle. Circulating anti freezing and anti condensation methods are mainly used for equipment and pipelines that are operated intermittently or not used for a long time, and the above methods (emptying, insulation, heat tracing) are not adopted for anti freezing, or the above methods cannot meet the anti freezing requirements. This method can be roughly divided into four ways:

first, the material at the outlet of the operating equipment flows back to the inlet of the standby equipment for circulation. This method is commonly used for antifreeze and anticoagulation of the standby dynamic equipment, such as through the bypass pipeline of the single valve at the outlet of the pump, or through the opening of the valve core of the single valve

second, it is connected to the equipment outlet pipeline through the equipment inlet pipeline. This method is commonly used to prevent freezing of the disabled heat exchange inlet and outlet pipelines. Connect the pipelines with small diameter in front of and behind the inlet valve of the heat exchanger to keep the medium in and out of the pipeline circulating

third, according to the normal operation mode, a small amount of circulation, generally try to close the outlet valve of the standby equipment as small as possible, reduce the medium circulation, and meet the antifreeze requirements

fourth, a small amount of medium is discharged continuously or intermittently. This method is mainly aimed at the failure of Panasonic exchange servo machine to establish the end of circulating pipeline for antifreeze, such as hose station, tank dehydration pipeline and valve, low point exhaust valve of steam pipeline, eye washer, etc

II. Antifreeze inspection

antifreeze inspection is an extremely important part of antifreeze work in winter. Regular antifreeze inspection can timely find and deal with problems in the process of antifreeze, and effectively avoid the further expansion of freezing blockage. Antifreeze inspection is mainly to check the effect of antifreeze and anticoagulation work, check leaks and make up deficiencies, and further improve antifreeze and anticoagulation work. The main inspection contents and methods are as follows:

1. The steam tracing pipeline regularly checks the drainage condition of the steam trap. If it is found that the drainage is abnormal, it should be checked and handled in time. If it is impossible to directly check the drainage condition (such as centralized to the drainage recycling station), you can use a temperature measuring gun or hand point to touch the valve body of the water drain valve (a detection hole should be reserved during insulation). Generally, the temperature should be above 30 ℃ or the feeling of hot is normal, Sometimes the feeling of warm and hot conditions does not necessarily confirm that the drainage is normal, especially for the situation concentrated to the drainage recovery station, because the nearby normal drainage pipeline conducts heat, it often misleads the inspection and judgment

2. For hot water tracing, check the water flow with a water flow indicator, or use a temperature measuring gun and hand to touch the electric heating band to reserve an inspection position to check whether the temperature of the electric heating band is normal; When the heat tracing hot water pipeline is recycled in a centralized way, it should also be based on experience to avoid the interference of heat conduction of the normal hot water pipeline due to accessories, which will affect the inspection and judgment

3. For electric heat tracing with temperature indication, not only the temperature indication value should be checked regularly, but also the inspection position should be reserved by touching the electric heat tracing band with a temperature measuring gun or hand to prevent inaccurate temperature indication and ensure that the temperature of the electric heat tracing band is normal. For electric heat tracing without temperature indication, the temperature should be detected

4. The enclosed plant should be equipped with a thermometer, regularly check the sealing of doors and windows and the heating temperature, and adjust the indoor heating volume according to the indoor temperature; Check the insulation and sealing of the valve well, and monitor its internal temperature if necessary

5. Regularly check whether there is material outflow and freezing blockage at the low point of the evacuated equipment and pipeline, or knock the pipeline with a wrench to judge. If freezing blockage is found, check the source of materials in time and deal with it accordingly

6. Regularly check the antifreeze circulation of equipment and pipelines. If there is a water flow indicator or mirror, observe whether the indication is normal; If there is no water flow indicator or mirror, use a temperature measuring gun or touch the equipment body or relevant antifreeze crossover by hand, and judge by temperature. If it is difficult to judge by temperature, you can also use a listening stick to judge the material flow of equipment or pipeline. For materials that adopt a small amount of discharge circulation to prevent freezing, regularly check whether the discharge capacity is normal

7. For instrument heat tracing, regularly check the sealing condition of instrument heat tracing box and the temperature condition in it. At the same time, according to the heat tracing method, check the instrument heat tracing according to the above methods; In addition, it can be judged whether the instrument is frozen and blocked by comparing the on-site and remote instruments and referring to the normal instrument indication value

8. Whether the rotating equipment is used for a long time or standby, it should be turned regularly to find out whether the equipment is frozen or blocked in advance; For equipment that cannot be cranked (such as canned motor pump), in addition to the antifreeze cycle inspection, the start-up should be carried out point by point, and the parts that are easy to freeze (such as the back seat of canned motor pump) should be measured, and then the start-up can be carried out after it is normal

9. The exhaust valve at the end of the gas (steam) pipeline, the exhaust valve at the low point of the U-bend, the valve at the hose station, etc. should be kept at a proper opening or regularly checked for drainage to avoid the accumulation of materials at the low point, resulting in pipeline freezing and blocking

10. For instrument gas, in addition to the regular drainage of the end of the main line and the low point, the water content in the main line should also be detected to avoid the accumulated freezing of the water in the instrument, resulting in the failure of instrument regulation

11. Regularly check whether there is water flowing out or freezing at the outlet of the discharged consumption facilities and the low-point discharge valve. 3. Due to the small risk of blocking in the establishment of the recycled plastic particle factory, if any problem is found, dredge it in time and confirm whether the root valve is tightly closed

12. Regularly check the system vent and breathing discharge ports, such as tank breather valve and flame arrester, emergency vent and pressure relief port, air compressor vent port, and boiler safety valve vent port to ensure that their vents are unblocked

13. Regularly check whether the inlet protection of outdoor fan, filter, motor and other equipment cooling and cooling fan is frozen and blocked. If there is steam emission around the equipment or in snowy weather, it is easy to be blocked

14. Regularly check whether the liquid in the water seal tank or liquid seal tank outside the room is frozen and blocked, and deal with abnormalities in time to ensure its proper function

15. In case of significant cooling or at night, strengthen the inspection, and adjust the heat tracing, plant heating and antifreeze circulation according to the temperature. It can't be done once and for all to avoid freezing and blocking

III. freezing and blocking treatment

in the process of thawing, it should also be treated in combination with the specific situation. Generally speaking, for small frozen and blocked equipment, short pipelines, instruments, valves, etc., the frozen and blocked surface can be directly purged with steam for dissolution, and if there is heat preservation, the heat preservation should be untied in advance; If the frozen and blocked equipment is large and the pipeline is long, the method of laying temporary heat tracing (such as metal hose) and thermal insulation is often used to thaw slowly. If the frozen equipment, pipelines, instruments and valves are easy to be removed, they can be removed and placed in a room with high temperature for thawing according to the situation

in order to avoid safety accidents such as toxic and harmful gases, liquid spray injury or explosion during the handling of freezing and blocking, the following points need to be paid attention to in the handling process:

first, check whether the freezing and blocking equipment, pipelines and valves are cracked or damaged and whether the valves are in the on-off state

second, relevant systems should be isolated before treatment

third, the operation should be slow and slowly dissolved with low-temperature steam to prevent sudden heating damage to frozen equipment, pipelines and valves

fourth, consider the impact on the instrument and process conditions after the sudden dredging in the thawing process, and take countermeasures in advance

IV. other matters

1. Combined with the antifreeze experience of previous years, deal with the antifreeze problems and prepare antifreeze substances, such as thermal insulation materials, steam traps, gold hoses, temporary joints, antifreeze gloves, etc

2. Prepare for a rainy day, put it into use in advance and check various antifreeze measures before winter, so as to provide enough time to deal with antifreeze problems and avoid sudden cooling, which will make antifreeze measures unable to be implemented

3. Adjust the heat tracing in time, not only to meet the needs of antifreeze, but also to avoid waste caused by excessive heat tracing, excessive process indicators, inaccurate instrument indications, etc

4. The material pipeline with heat tracing should have an expansion direction to avoid the pressure holding of equipment or pipeline caused by the heating and expansion of materials. If there is a pressure gauge, pay attention to monitoring its pressure

5. The material pipeline is in the running flow state, and the heat tracing pipeline and its heat tracing