Process Economics Program Report 174A
High-Output Fluidized Bed Polyethylene Technology
Published: June 1996
This report deals with the technology and operating economics of producing linear low-density polyethylene (LLDPE) by high-output, gas-phase fluidized-bed technologies. In commercial practice, gas-phase plants are dedicated to the production of LLDPE or high-density polyethylene (HDPE; alternatively, plants may produce both LLDPE and HDPE in a blocked out mode (swing plants). The scope of the report is limited to the production of the butene-1 copolymers of LLDPE.
The principal suppliers of high-output technologies are Univation, a joint venture of Union Carbide and Exxon Chemicals; and BP Chemicals. Univation�s high-output technologies are called the Condensed and Supercondensed Modes; and BP Chemicals� are called the Innovene® High Productivity and Enhanced High Productivity technologies.
High-output technologies are characterized by the cooling of reactor effluent gases below their dew point to allow the recycle of a mixture of liquid and gases. The heat of vaporization of the liquid in the recycle stream enhances the removal of the heat of polymerization, thereby increasing reactor output.
We have developed representative operating economics for the Univation and Innovene® technologies, based on the production of C4-LLDPE with a melt index of 0.92 and a density of 0.91�0.92. For Univation�s process, we have selected the following capacities and modes of operation:
- 441 million lb/yr (200,000 t/yr), dry mode
- 705 million lb/yr (320,000 t/yr), condensed mode
- 1,103 million lb/yr (500,000 t/yr), supercondensed mode.
For Innovene®, we developed economics for a 705 million lb/yr (320,000 t/yr) high-productivity plant. We compare the economics of the Innovene® and Univation technologies for a 320,000 t/yr capacity. We also analyze the economics of doubling the capacity of a 200,000 t/yr dry mode Univation plant by line duplication and by switching to the supercondensed mode.
We conclude that the Univation process has a slight advantage in operating economics, which derives from a lower investment (about 3%) and lower raw materials costs. For capacity expansions, the favorable economics of high-output expansion are quite apparent: The incremental battery limits investment for the supercondensed option is approximately 65% of the corresponding figure for line duplication.