The safety hazards and design optimization of coating chemical equipment

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There are two ways to solve the problems of far-infrared heating: firstly, in terms of operation, turn off and stop the far-infrared heating appropriately before the end of the reaction, and use the remaining heat to continue the reaction.
To cool down after the reaction, the residence time of the materials in the kettle should be appropriately extended, so that the heater cavity and the wall temperature of the reaction kettle are as close as possible to the material temperature.
This can save energy and achieve a multiplier effect.
Of course, there is no such problem in the operation of the positive dilution production process.

In terms of equipment design, a forced ventilation system with a far-infrared jacket is added to directly ventilate and cool the far-infrared jacket and the wall of the kettle.
Such disposal will effectively solve product quality problems, and more importantly, ensure safe production.

The far-infrared heater has another fatal flaw.
This is the problem of oxidation and changes in the structure of metal materials in the resistance band after long-term use at high temperatures, especially the internal connection of the heat-conducting band.

This will cause partial overheating of the resistance band and eventually cause a circuit break.

Heat conduction oil heating has obvious advantages such as rapid temperature change and no local overheating.
However, the ordinary heat transfer oil heating process has the problem of high energy consumption for the intermittent heating and cooling process.

This is because the hot oil in the jacket (or coil or half tube) must be cooled when the reactor is switched between cold and heat, and the cold oil must be reheated.

There is a noteworthy problem when using heat transfer oil for heating, which is the thermal expansion of the heat transfer oil.
The expansion coefficient of heat transfer oil is an important parameter of heat transfer oil.

The larger the expansion coefficient, the better the heat transfer effect of the heat transfer oil.

Figure 2 Reactor heating and cooling system

In fact, there are also many safety problems due to process operation and material properties.
For example, when the water content of polyester resin and other viscous materials is relatively large, the temperature is too fast or the vacuum is dehydrated, especially when the vacuum is suddenly pulled up, the solvent and other low-boiling substances in the reactor will be produced under reduced pressure.
"Flashing" and violent vaporization, resulting in pot expansion and overflow; when phthalic anhydride is put into high-temperature materials, it will also cause expansion and overflow due to sublimation.
This kind of pot expansion and overflow will bring great danger to safe production.
Of course, it is not difficult to avoid these hidden safety hazards in operation.
Avoid too high temperature in the kettle when feeding, pay attention to observation, and slowly feed; pull the vacuum while observing.

For those high-risk reactions with relatively large and sensitive thermal effects, it is necessary to meet the requirements of cooling and removing heat from the system design, such as choosing a slender and relatively large reactor to obtain more specific surface area (jacket) for cooling.
Add cooling coils when necessary; cooling medium (cooling water) channels should fully meet the cooling requirements; when accidents occur, the relief channels (passive relief valves, active relief vent pipes) should be short and smooth, and when necessary It is necessary to set up anti-splashing and entrainment cyclone separation, recovery and treatment facilities to avoid environmental pollution and secondary accidents.

For those reactions where initiators are added, there is generally an initiation process.

The instrument is the eyes of the operator, and the automatic control system is the reaction center of the adjustment and control of the device.
Practice has proved that automatic control plays an indispensable role in safe production.

For high-risk response systems, automatic alarms, precise adjustments, and interlocking disposal are more necessary.

In terms of the structure of the reactor, the outer half pipe is now generally used instead of the jacket.
The heating of the outer half pipe has obvious strength advantages over the jacket.

After the jacket of the reactor is changed to an ordinary half tube, there is a problem of insufficient heat transfer area, but the heating area of ​​the full half tube heating reactor is exactly the same as the jacket heat transfer area, and the heat transfer is faster! Higher thermal efficiency!

1.
Structural features-half pipes cover each other.

Compared with ordinary half pipes, half pipes require high rolling processing, but the welding construction quality is stable and reliable.

2.
The heating area of ​​the full half pipe is the same as that of the jacket, which is much higher than that of the ordinary half pipe.

3.
In addition to the high heat transfer coefficient, which is conducive to heat transfer, structurally speaking, the ability to withstand internal and external pressure is greater.
Under the same operating pressure, the wall thickness of the reactor can be reduced, thereby reducing equipment manufacturing costs .

4.
The heating area of ​​the equipment is adjustable.
The half-pipe heating can be divided into several groups, according to the level of the material in the reactor and heating (or cooling) needs, you can choose to close or open several groups.

There is a problem to pay attention to after changing the jacket of the reactor to the outer half pipe.
That is because the lower head is limited by the difficulty of processing, it is difficult to realize the transformation of the full half pipe, resulting in the lack of heating area at the bottom, the second is the large heat capacity of the valve seat and valve, and the third is the use of solid materials such as dibasic acid in the resin production.

, Deposited on the bottom of the reactor, requiring a lot of melting heat.
This will affect the melting, mass transfer and reaction of the material, and even the residual raw material, which will affect the quality of the product, and will also cause the lower discharge to block and affect the opening of the discharge valve.
For users who put in solid reaction raw materials, a small annular jacket is designed and processed at the bottom of the reactor (as shown in the figure).
One side of the jacket is connected with the half pipe, and the other side is the inlet (outlet) of the heat medium.
mouth.
The heat medium, such as heat transfer oil, enters the half pipe directly from the small jacket, so that this problem can be easily solved.

three.
Stirring design of reactor

Another feature of resin production is that the material viscosity is relatively large, especially in the late stage of the reaction.
How to strengthen the mass transfer of viscous materials in the resin reactor, remove the water produced by the reaction, and promote the in-depth progress of the esterification reaction.
How to realize the two circulations (axial and radial) of the material in the reactor, ensure the homogeneous reaction of the material, promote the renewal of the micro-particle interface of the material, increase the reaction speed, and shorten the reaction period.
Stirring is the key!

Here we recommend a traditional frame mixing, which can be achieved with a little modification-rotating the horizontal blade and the vertical blade at an angle.
The vertical frame allows the material to flow from the periphery to the center, and the horizontal frame allows the material to flow from top to bottom, thereby realizing two circulation and cross flow, which improves the mass transfer of the material and reduces the wall formation of the polymer.
Of course, we can also use frequency conversion speed adjustment as needed, and the adaptability and selectivity of the stirring speed will be further improved.

four.
Auxiliary facilities and others

Chemical companies have many platforms.
Whether it is a concrete operating platform or a steel platform, it is absolutely necessary to prevent objects (such as wrenches, screws, nuts, etc.
) from falling from a height.
Especially for steel platforms, the friction is relatively small.
Setting a fall prevention baffle (as shown in the picture) under the railings around the platform can get twice the result with half the effort.
Of course, the wearing of the helmet should not be neglected.

To put it in an exaggeration, if safety production is taken lightly, chemical companies like paint production are almost everywhere "explosive barrels" and "landmine arrays".
For example, there are vats for raw materials and finished products almost everywhere, and the remaining solvent and air form an explosive mixture.
The construction workers often used it as a scaffold when welding.
The ground wire and welding handle wire of the welding machine accidentally damaged the insulation rubber and hit the vat.
With a "boom", the vat flew out, scaring the construction workers to wake up for a long time.
But God came, fortunately there was no accident in life.

In addition, there are hidden dangers like underground ditches and sewer pipes.
Solvents and organic monomers used in coatings are generally lighter than water and volatile.
Spilled drips in transportation and production will directly or indirectly enter the trenches and sewers.
Over time, the inexhaustible drainage wells of the sewers, especially those whose water level is higher than the top of the pipe, have actually become oil-water separators, causing the accumulation of organic matter such as solvents, and the above can easily form explosive gases with the air.
On-site welding construction, sparks splatter all over, accidents will happen if you are not careful.
For these situations, one is to arrange timely cleanup, and the other is to strictly prohibit fire in the surrounding area.

In short, safe production is an important policy of the country, which is related to the survival and development of enterprises, and is the guarantee of employees’ lives.
It must be emphasized ideologically, guided by scientific theories, fully identify hazards, and download hardware and software at the same time.
Kungfu must not be taken lightly and indifferently.