6 replies to this topic

[krishna unni]

I am working for LDPE plant having autoclave process. Now our reactor bottom temperature is maintaind at 295 degree C(last zone temperature is at 285 Degree C. I would like to raise bottom temperature to higher as to reach higher conversion. Is there any LDPE autoclave plants in the world which is having a higher bottom temperature than 295Degree. pls let me know.

[sheiko]

I am working for LDPE plant having autoclave process. Now our reactor bottom temperature is maintaind at 295 degree C(last zone temperature is at 285 Degree C. I would like to raise bottom temperature to higher as to reach higher conversion. Is there any LDPE autoclave plants in the world which is having a higher bottom temperature than 295Degree. pls let me know.

It is indeed true that, in the high pressure autoclave process, the reactor operates adiabatically and, as a result, the conversion rate is directly proportional to the difference of temperature between the in-going and the out-going flows: m*Cp*(Tout-Tin) = m*X*dHr (X = conversion rate, dHr = heat of polymerization). dHr is close to 800 kcal/kg_{_LDPE} and Cp of ethylene close to 0.6 kcal/kg/°C.

Don't forget however that this conversion rate is limited (to about 18%) by the maximum acceptable temperature of the reactive media because of risk of ethylene decomposition or control of product quality. The decomposition reaction is highly exothermic and leads to VIOLENT EXPLOSIONS.

Moreover, the temperature necessary to initiate the explosive decomposition drops very rapidly as the pressure rises, which makes the HPPE (High Pressure Polyethylene) process very "decomp prone". Try to find these tables showing this temperature dependance on pressure. Of course, nominal process conditions are selected in such a way that they NEVER cross the decomposition limits.

PS: HPPE and LDPE (Low Density Polyethylene) are synonyms. One refers to a characteristic of the process, the other to a characteristic of the product.

Edited by sheiko, 20 July 2011 - 09:03 PM.

[GS81Process]

I am working for LDPE plant having autoclave process. Now our reactor bottom temperature is maintaind at 295 degree C(last zone temperature is at 285 Degree C. I would like to raise bottom temperature to higher as to reach higher conversion. Is there any LDPE autoclave plants in the world which is having a higher bottom temperature than 295Degree. pls let me know.

Sheiko's response is accurate.

We do not run bottom zone temperatures above 295C due to the decomposition risk. I am not aware of anyone running LDPE bottom zone beyond 295C.

Edited by GS81Process, 11 July 2011 - 02:19 PM.

[krishna unni]

thankyou sheiko for sharing information, my question was directly pointing towards the reactor botom zone and reactor bottom temperatures. if you are working with LDPE please share the zone temperatures and feed temperatures which you are maintained in optimum.

[sheiko]

thankyou sheiko for sharing information, my question was directly pointing towards the reactor botom zone and reactor bottom temperatures. if you are working with LDPE please share the zone temperatures and feed temperatures which you are maintained in optimum.

Sorry, I don't work in a LDPE plant but in a refinery, so I don't have this piece of information.

PS: "T_out" that I have mentionned in my first post is precisely the reactor bottom zone temperature.

Edited by sheiko, 20 July 2011 - 09:05 PM.

[GS81Process]

thankyou sheiko for sharing information, my question was directly pointing towards the reactor botom zone and reactor bottom temperatures. if you are working with LDPE please share the zone temperatures and feed temperatures which you are maintained in optimum.

We run different grades of LDPE with different bottom zone and feed gas temperatures depending on the grade. However, we do not exceed a 295C bottom zone temperature for any LDPE polymer due to the safety risk of approaching the decomposition boundary.

Edited by GS81Process, 21 July 2011 - 09:21 AM.

[Mannus]

I work in a LDPE Autoclave plant, we can´t increase bottom temp because it's too dangerous. The temperature donwstream the reactor would rise due reverse joule-thomson effect on the extrusion valve. The lowest feed temperature is 27°C, but you risk loosing reaction in the first zone, so for this one you have to go higher.