Application-development Of Condensing Mode Technique In Daqing LLDPE Equipment

The advantages and feasibility of condensation state operation in LLDPE unit are. introduced. Compared with the gas phase method, this technique leads to the following advantages: Operation flexibility of the unit increases; Capacity of the unit increases without replacing the key equipment including reactor and recycle gas compressor. Change of the technology is little and operation is easy. Easy switch between the normal state and the condensation state operation. A novel technical development on Condensing Mode, Super Condensing Mode, Liquid Monomer Polymerization Mode and indirect cooling reactor of the process of gas-phase ethylene polymerization of was summarized. The latest research results and the published patent literature are reviewed about the process of polyethylene in gas fluidized bed by named Condensed Mode Operation. The principles and methods of the design of gas and liquid flow deflectors and atomizer/spray nozzles have been demonstrated in the fluidized bed. It discusses in detail the relationship between the process operation conditions and the quality and yield of pro duct. It is further elucidated that the polymerization process using metallocene catalysts system in a Condensed Mode would be an optimal process route.An investigation to the increase of capacity of removal heat from ethylene polymerization in gas-solid fluidized-bed reactors, with addition of inert medium which is apt to be condensed, was carried out in this work. With a suitable thermodynamics model, a simulation was taken to investigate the effects of various fraction of various inert medium on the heat properties of polymerization system. It is likely reasonable that based on the operating conditions there are three possible types of modes, i.e., single temperature rising, partial and total evaporation of DIPC, existed in the gas-phase fluidized bed reactors in using condensation mode for ethylene polymerization. By taking Unipol process as a example for gas-phase ethylene polymerization in fluidized-bed reactors operating with condensed mode, a simulating approach was developed to study the effects of the dew point and compositions and temperature of the recycle flow entering in the reactor on running states of the fluidized-bed under different conditions o f productivity in this paper. The disadvantageous effects of the liquid contained in the recycle gas were also discussed.A novel two-phase model for the fluidize bed of polyethylene with condensed mode operation was proposed. The model considered heat and mass conservation in emulsion phase and bubble phase, heat and mass transfer between emulsion phase and bubble phase, polymerization as well as resident time distribution of particles in emulsion phase. The relations between operating variables and reactor performance were investigated by the model. Simulation results agreed well with the industrial data. Simulation results indicate the productivity of reactor as well as ash in polymer will increase greatly, and low the temperature region will expand when the condensed mode is operating with the conventional catalyst. A type of catalyst which suits condensed mode operation was proposed.A heat and mass transfer model across the external boundary layer of polymer particles in emulsion phase with condensed mode operation was derived. The overheat possibility of particles was analyzed by using the model. Simulation results indicate that in the early lifetime, there exist multi-steady states of surface temperature of growing particles. Using the condensed mode operation will be helpful to reduce the temperature gradient for larger particles, but not for very small particles. The type ofcatalysts with a low startup, high activity and high quick deactivation was suggested to be used in the condensed mode operations.LLDPE plant was put into production in July 1988 in Daqing. It is the first LLDPE plant in domest ic and its designing ability is 60kt/a, runtime is 8000 h/a. In 1999,because expansion output reforming of ethylene cracking equipment in Daqing Petrochemical Complex, ethylene output is going to reach 480,000 tons. In order to match with its output and material balance in complex, we put forward a goal of 840kt/a ethylene. So we decide to execute expansion output reforming to LLDPE plant in Daqing. After feasibility study of introducing condensing technique in LLDPE plant in Daqing, consulted a lot of theory study literature on condensing mode technique, defined usable condensing material in Daqing plant, made a theory calculation of dosage of condensation material and removal heat ability of reactor, and reformed related equipments to meet the need of expansion output. Twice developing experiment and once industrialized applying experiment on condensing mode technique was made in Daqing LLDPE plant.The main contents of application development of condensing mode technique in Daqing LLDPE plant include: 1) choosing condensation materials and analyzing the relation between liquid-phase quantity and STY. Combining the weather characteristics of the native area, establish the homologous operation parameter scope for different yield.2) the new catalyst mixing machine was developed, blend together the catalyst of the different model number equably using it , produced the appropriative catalyst that be applicable to the condensing mode operation, guaranteed the stability of the product quantity and the operation.3) the method of a stability operation was investigated, insuring fluidized bed reactor continue to run.4) find out the device bottleneck in expanding output ,in order to make use of condensing technique as well as possible.In March in 2000, took industrialization big production in the condensed mode in Daqing LLDPEplant. The yield of Daqing LLDPE plant increases from the 7.5t/h of the original design to 10.5t/h now,the tallest moment load attain 13 t/ h, coming to the target level of increasing reactor produce ability by 70% in condensing operation in UCC plant. There are some questions on applying condensed mode operation in Daqing LLDPE plant. These questions restrict the production on a large scale. At present, the production burthen in Daqing LLDPE plant can attain only a 140% of design. To make the production burthen in condensed mode operation attains a 170% of the design capacity, we must reform the exhausting system of the row and gas, increasing these two systems ability. Since putting the condensed mode operation to use, the increasing production burthen of Daqing LLDPE plant bring a benefit of 43,543,100RMB through 30 months after producing.