Heat Integration Study on Cryogenic and Product Recovery Unit of Gas Processing Plant

The production and consumption of natural gas is on the rise throughout the world as the
result of its wide availability, ease of transportation and use as well as clean burning
characteristics. The first and second generation gas processing plants, designed and built
in the 1960s and 1970s were bogged down by operational inflexibility and CO2 freezing
due to the rapid change of product values. Even most modern gas processing plants are
encountering problems related to operating flexibility, instability of operational
conditions due to vapor-liquid equilibrium, CO2 solid formation and energy efficiency.
Ortloff have recently developed new NGL recovery processes on the basis of vapor-split
concept. While the Ortloff processes offer relief to the first three problems in gas
processing plants, huge energy consumption remains a major concern. A typical gas
processing plant consists of two main processing sections, i. e. a cryogenic section and
product recovery section. Of the two sections, cryogenic section consumes a huge amount
of energy, especially by its cold utility due to the sub-ambient operating condition
required. Meanwhile, steam generation for reboiling purposes at the product recovery
section also contributes to the huge energy consumption. Ultimately, both result in
substantial utility cost to the plant operations; therefore optimizing energy consumption
in both areas is essential to improving plant profitability as it results in lower utility cost.
This research looks for improvement opportunities in energy consumption in these two
sections based on pinch analysis and maximizing the power generated from turboexpander.
The study explores the utilization of available cold energy extracted from the
feed in order to reduce the cold utility requirement in cryogenic area. The study is able to
save 6% on refrigeration load for cryogenic area and generate 36% more power from the
turbo expander. This could generate predicted annual savings of RM900k for this area.
For product recovery area, this study introduces a prefractionator arrangement in place of
a conventional depropansier and debutanizer arrangement. Although thermal coupling
arrangement requires refrigeration for condenser cooling, nevertheless it generates 54%
savings on steam consumption and 37% savings on cooling duty. This is equivalent to
RM 2.9mil as predicted annual savings for the plant. Moreover, there are some loose end
heat exchangers that could give about RM350k savings per annum for operating cost.