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1 Inżynieria Chemiczna i Procesowa

1 2002

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Analiza strat egzergii jako podstawa usprawnień układu chłodzenia gazów pirolitycznych w instalacji olefinowej

Budek A., Markowski M.

Inżynieria Chemiczna i Procesowa

2002

T. 23, z. 2

277-290

Olefin pyrolysis is the example of cracking under very high temperature, where mixtures of gases are obtained. The gases are then separated in a cryogenic system. Whilst the process of pyrolysis takes place under 900 degree C, the separation is processed even below -100 degree C. The cost of obtaining so low temperature is very expensive in olefin plant. The temperatures below ambient are obtained in propylene refrigeration system - four levels of temperature (the lowest temperature is -40 degree C, Fig.2) and ethylene refrigeration system . three temperature levels (the lowest temperature is -102 degree C, Fig.3). These propylene and ethylene systems have been analysed using Pinch Point Technology method. Exergy analysis has been also used. The maximum heat regeneration in thermodynamic system as well as the minimum consumption of external energy and minimum waste heat have been obtained.Input data (heat capacity, inlet and target temperatures, mass flow, etc.) of 59 process streams (tab.1) and 8 utility streams (tab.2) have been collected. UCC curves have been obtained and used in exergy analysis of the existing cryogenic system for olefin plant. Four variants with regard to the assumed number of the temperature levels have been defined. Adopting entropy increase and exergy loss as the objective function, temperature values (at the individual levels) corresponding to the minimum of objection function were determined for each variant (tab. 3 and tab. 4). The exergetic efficiency of refrigeration systems as well as the decrease in power of turbines driving the expanders of propylene and ethylene refrigeration systems have been calculated. The decrease 5.6/13.5 % in exergy loss as well 2.2/5.2% in power consumption have been obtained for the analysed variants (tab.5).