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Introduction to Compressor Types

IP.com Disclosure Number: IPCOM000221652D
Publication Date: 2012-Sep-14

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~The M.Wo Kellogg Company

GAS CRACKING CHARACTERISTICS IN THE COMMERCIAL RANGE OF OPERATIONS

By :


R, Orriss


J. H. Dluzniewski


A. P. Moore

THE M. W. KELLOGG COMPANY Houston, Texas

Presented At:

AMERICAN CHEMICAL SOCIETY

SESSION

Seattle, Washington

March 21, 1983


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~The M.W. Kellogg Company

DRAFT

GAS CRACKING CHARACTERISTICS IN COMMERCIAL RANGE OF OPERATIONS

Introduction

   Ethane and propane, which are excellent feedstocks for pyrolysis, are available in many parts of the world in natural gas resources. They will probably form the basis of developing petrochemical industries in areas such as

Africa, Indonesia, South America and the Middle East, and are still important olefins feedstocks in the U.S.A.

   Although the cracking of pure components involves an appreciable number of reactions, it is not nearly as complex as liquid cracking. Nevertheless, the selection of optimum yield targets is not straightforward. Tile profitability of an olefins plant is greatly influenced by the severity and selectivity at which cracking takes place.

   Qne purpose of this paper is to identify the economic driving forces which dictate optimum cracking conditions, with some indications of the magnitude and direction of these driving forces.

Pure Component Cracking

   When discussing pure component pyrolysis, the severity of cracking is readily indicated by the quantity of feed which remains unconverted after passing through the pyrolysis reactor. In commercial units which use ethane or propane feedstocks, any unconverted feed is easily recovered in the distillation section and is recycled to the pyrolysis furnaces. In this way~ total conversion of the feedstock is effectively obtained. This type of


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~The M.W, Kellogg Company

operation leads to consideration of the "single pass" yield, the "ultimate"
yield and the recycle flows in selecting the severity of cracking. These terms can best be explained by considering the mathematics of a simple ethane
cracker. Figure ! illustrates a simplified approach to calculating the
ultimate yield and recycle flows for an ethane cracker. In practice, the gain
of ethane from acetylene hydrogenation and the loss of ethane in ethylene and propylene product Streams is accounted for in detailed materia) balances but the Figure i simplified approach serves to show the major trends without entering into the complications of linear programming. The ultimate yield is essentially the effective overall material balance yield, while the single pass yield is simply the furnace material balance. By investigating the yields over- a range of feedstock conversions, it is possible to show the interrelationship of these factors.

Ethane Cracking

   Variations in feedstock consumption and plant throughput for a 250,000 MTPA ethylene unit using pure ethane feedstock are shown in Figure 2. Curves are shovm representing typical current cracking conditions and a more selective condition which would be achieved by using a much shorter...