HOW EXACTLY TO Control Your CO2 in XPS Production Line

It is well known that CO2 may be the most challengeable blowing agent to handle during the physical foam extrusion process. It really is for reasons. For example, the supercritical stage, touchy dry glaciers, and its own density differ when circumstance temperatures changes etc apparently. For end clients, understanding this information wouldn't normally anywhere get you. You still need dependable design to warranty the productivity of your production line. I am not likely to tell you many terminologies or theories. I just desire to share our practical knowhow of managing CO2 in XPS production. To better understand the techniques at each device of the complete system, let’s start from explanation of our flow chart. The following chart is not the real PID, it is just a sketch which will help you understand the way how exactly we control the CO2. The actual PID is a lot even more complicate than this which involves tens of valves plus some additional accessories.



Normally industrial use CO2 is delivered simply by truck that carries tens of a great deal of liquid CO2. As well as the CO2 shall be stored in a huge vacuum insulated tank which is generally 25 lots approximately. The temperatures of CO2 inside of the tank is approximately minus 20 level Celsius, as well as the pressure is certainly between 1.6-2.0Mpa. Once the environment heat range transformation causes the pressure rise, the tank will give off CO2 to cool off itself.

You may already know that water is much better to hands than gas. So we have been gonna manage to keep CO2 within the state of liquid during the whole procedure. Because the CO2 is very prone to vaporize because of its high vapor pressure, therefore we have to hit the total amount between pressure and heat range. This is the basis of how our bodies works.

We employed a booster pump that may transport the water CO2 from CO2 container to middle tank whose wall was jacketed style, where the heat of the middle container could possibly be controlled by drinking water temperature controller. One tip I have to take it up here is that the length between CO2 tank and middle container must be as near as you possibly can. Due to the propensity is got from the CO2 of vaporizing so that the longer range, the more risky to vaporize. To take action, the booster pump is preferred to put beneath the CO2 tank. Even so, the vaporizing still occurs occasionally. When the booster pump struggles to pump properly the CO2, vaporizing happened probably. The release valve is made for this situation, so open it and discrete the vaporized CO2 in order to cool down the temp of the head of the booster pump. This process must cautiously be achieved very, because if the release valve is certainly opened too much, the CO2 is liable to become dried out ice that may block the pipe, and it will take long time to melt off. To avoid this situation happen, the capability from the booster pump ought to be ten times larger than metering pump so that the booster pump doesn't have to operate on a regular basis, only works periodically. Besides, longer release pipe is advised which could prevent the inlet tube of booster pump from freezing by dry ice. In addition, the insulated piping of the whole program shall contribute to the consistence of CO2 transport, it can conserve energy also.

The goal of middle tank would be to keep the CO2 at a particular temperature (around 25 level Celsius) to be able to keep up with the pressure of the whole system is stable and high enough (6.5-7Mpa). Both of these premises guarantee the continuous physical house of CO2 and it gets CO2 primed for exact metering into twin screw extruder. As I discussed earlier, the density of CO2 varies when temperatures changes. The best level alarm of CO2 in the middle tank should be no more than 70% of the total volume of the middle tank in case of any incident occurred, the billed power slice in the summertime in some hot region, which may trigger circumstance temperature of middle tank goes high, then the CO2 could become supercritical condition whose behavior is usually more difficult to regulate and predict. As a result the quantity of CO2 is going to be extended significantly. If the free space is not enough, it may obtain the plastic compounding machines center tank in some danger.

Before CO2 switches into middle tank, it'll be warmed up to ensure the temperature of CO2 in the centre tank at a particular degree as it is intended. It really is 25 degree Celsius normally. At this heat range the pressure of middle container is about 6.5Mpa. Exactly why is it to be established at this temperature? In many countries, 10Mpa is a watershed to separate high pressure vessel and very high pressure vessel. The second option requires complicated certificates and more costly. So 7Mpa is safe for high pressure vessel. After going through the middle tank, the OO2 goes into another cooling vessel which will bring the heat range of CO2 right down to 10 ten level Celsius. Now the circumstance of 6.5Mpa and 10 degree Celsius help to make the CO2 in pure water. And the more liquid, the easier to dose. CO2 within this state can be metered into the principal extruder (twin screw extruder) easily. A very important factor has to be addressed would be that the pump mind has to be cooled by way of a chiller. Once the pump heads are working, it shall generate some high temperature which can make liquid CO2 vaporized that will problems the procedure.

When all above mentioned points have been taken care of, it cannot warranty that the CO2 can be handled correctly even now. If any section of piping traps vaporized CO2, this system would not work properly. One thing you must do is to open up the discharge valve with great focus on avoid big dry ice occurs. The release valve before injection valve is recommended strongly. When you start to see the white smoke (small contaminants of dry ice) comes out, there you decide to go, close the valve just. Today the CO2 is normally working out.

That is our way to regulate CO2 system. This is actually the combination of considering China-made, economic, dependability and practical. There are a few different ways can control CO2 very well also. Such as, LINDE PRESUS and DSD package are designed for the CO2 exactly as well. Our system is dependant on the condition of made-in-China simply. According to our long time experience, China-made piston pumps are no issue in any way in handling CO2. The drawback of piston pump is that the risk of leakage of China-made is normally larger than membrane pump as time passes. But CO2 is usually nontoxic and nonflammable; it doesn’t make sense to be worried about this risk. Moreover, the sealing stuff is very inexpensive and available. Changing sealing stuff can be put as a routine into the maintenance function. Nevertheless, the flammable blowing agent like HFC152a, ethanol, DME, Isobutene etc. is better dealt with by membrane pump.

Our foam extrusion lab is using another program that may deal with little volume CO2 perfectly. But it is only for lab use now. This system cools the CO2 down to minus 20 degree Celsius to help make the CO2 in the state of natural liquid with a little pressure. Normally this technique works with a CO2 cylinder which contains tens of kilos of CO2 just. It really is fairly inexpensive and easy to function.

All in all, it is best to keep the CO2 in the condition of pure water during the entire handling process. As to the so-called supercritical CO2 foam XPS production line, for the reason that the CO2 becomes supercritical state when it's injected into the barrel where in fact the temperature is around 200 degree Celsius. The real name has nothing to do with the handling process.

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