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.