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Safety issues in the process of material input in the production process of chemical industry when using reactor

By Thomas Huang March 20th, 2024 130 views
Generally, there are three ways to feed: 

I Pressure feeding

1.1 Gas feeding

Most of the gas raw materials are fed by pressing method.  
The pressure need to be controlled while feeding.  The gas need to through pressure reducing valve after get out from cylinder.
The pressure difference between the gas inside and outside the reactor should not exceed 0.15MPa. So, it could prevent the gas flow rate from being so fast that form a strong jet at the outlet and generating static electricity. 
Before injecting flammable gas, the air inside the reactor need to be evacuated by negative pressure, or purging with inert gas like the nitrogen.  The parts inlcuding reactor, pressure tube, and platform or scale for gas cylinder need to be grounded.  Pressure feeding pipeline shall apply large diameter, to ensure a slow pipeline gas flow rate.

1.2 Liquid feeding

We can use header tank to feed liquid into the reactor by the effort of gravity.  It is not high pressure and flow rate is normal, so it is relatively safe.  However, when the reactor has high pressure, it is necessary to pressurize the feeding. 
At this time, if it is a flammable liquid, inert gas should be used for pressure feeding. Compressed air should not be used to prevent the formation of explosive mixtures.  If pumping is used, special pumps for transporting flammable liquids should be used, such as Y-type liquid hydrocarbon pumps.  Steam reciprocating pumps are also safe. 
If using the ordinary centrifugal pumps or gear pumps, their impeller must be made of non-ferrous metal to prevent sparks from occurring when the impeller collides with the iron shell.
There are many cases of exlosion accidents occured by using ordinary pumps to transport flammable liquids.  
Due to poor conductivity of ceramic pump and glass pump , it is easy to generate static electricity, so they shall not be used to transport flammable liquids.  
The outlet of the pressurized feeding device is preferably flared, which can reduce the flow rate at the outlet, avoiding the violent spraying generates static electricity. 
The equipment shall not leak and grounded is needed. 

II Vacuum feeding

2.1 Powder feeding

Powder or small particle materials should not use compressed air feeding to avoid dust flying.  
When using vacuum feeder with negative pressure pumping, it is relativly safe.  During material extraction, the equipment is connected to vacuum system, and filter screen or water washer shall be installed at the inlet of vacuum pipeline from reactor to prevent dust from being pumped into vacuum pipeline.
If the suction pipe is an insulator, the inner and outer walls shall be lined with spiral copper wire, and the copper wire mesh and reactor shall be grounded.  
If conductor piping is used, copper wire mesh can be omitted, but grounding is still required.  
If there are flammable liquids with low boiling points in the reactor, it is not advisable to use negative pressure pumping method. 

2.2 Liquid vacuum feeding

 Liquid raw materials can generally be fed by negative and pressure pumping methods, and the entire pumping system should be grounded.  
When pumping materials, the feed pipe should be inserted into the bottom wall of the reactor, the pipe diameter should be large, and the flow rate should be slow. 
If it is a flammable liquid with a resistivity of 1010~1015, the flow rate should be limited, and the initial velocity should be controlled within 1m/s, because the mixture of flammable liquid vapor and air existing in front of the flammable liquid at the beginning of transportation will explode in case of electrostatic spark.  
It is forbidden to spray liquid on the liquid surface to avoid static electricity. 
When flammable liquids are fed by suction, the temperature of the liquid should be at least 30 ° C lower than the boiling point.  
When the liquid temperature is high, it should be cooled first and then pumped to prevent a large amount of liquid gasification loss, resulting in inaccurate ratio and abnormal reaction and fire hazard.

III Manual feeding

3.1 Types of feeding material

Flammable and toxic liquid raw materials should not be poured manually.  
Solid material can use both suction method and manual methord, and the manual methord is the most commen one. 

3.2 Feeding order

The feeding sequence should meet the requirements. In principle, the feeding acted at low temperature.  And heating could only be done after all the feeding is finished, if the heating is required.  
If there is water in the raw material, on the premise of not affecting the reaction, water should be added first, then solid, and finally flammable liquid.  
If there is no water, solid materials should be added first, followed by liquid materials, so as to avoid a large amount of flammable liquid vapor escaping when feeding. 

3.3 Notice of feeding solid material into flammable liquids

If the solid materials are contained in bags made of synthetic fibers or plastic film, they shall not be used to directly charge the reactor, in order to prevent the risk of electrostatic sparks caused by friction.  
The material should be poured into the barrel first, and then poured into the reactor from the barrel.  
It is forbidden to wipe the residual powder at the mouth of the kettle with nylon cloth and other synthetic fiber rags with high resistance and low water absorption to prevent electrostatic sparks.
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