(25c) Waste Heat Recovery Considerations in LNG Plants

WASTE HEAT RECOVERY CONSIDERATIONS
IN LNG PLANTS

ABSTRACT

DOUGLAS WILES, RYAN HOLLENBACH &
STANLEY KWAN

Thermal integration in an LNG plant improves its overall
thermal efficiency. Thermally integrated plants tend to have lower operating
costs and reduced environmental emissions including, CO, CO₂, and NO_x.

Waste Heat Recovery Unit (WHRU) viability will depend
on project specific factors including the availability of waste heat, type, quality
and cost of fuel, type of heating medium and environmental regulations. The scope
of the project, for example whether it is a green-field or retrofit
construction, will determine the relative importance of many of these factors.

WHRU installation is a capital intensive process. The
economic viability will depend on the magnitude of the accrual of operating
cost savings, and their ability to counteract the initial capital outlay.  Savings can be in the shape of reduced fuel
gas costs, reduced emissions, and increased LNG production. Ultimately the
impact of these savings will depend on the owner's measurement of the value of
fuel gas; whether fuel usage is accounted for as lost feed or lost product.  The negative impacts include the reduction in
nitrogen rejection that occurs with reduced fuel gas usage and the power
restrictions imposed on gas turbines due to the increased back-pressure caused by
the presence of the WHRU.

This paper investigates the factors impacting the
viability of WHRU in an LNG plant and identifies scenarios where WHRU equipment
can add value to a plant. A real world case study will be used to quantify the
impact of these variables on the cost of the WHRU.