Improve Plant Efficiency with Waste Heat Recovery
In the process industry today, where environmental sustainability is becoming and increasingly important driver in plant decisions, operators need to focus on any means available to reduce energy consumption.
In oil and gas refineries, for instance, a great deal of energy is often consumed to heat and cool product streams between stages. Sugar production is also extremely energy intensive, as vast amounts of heat are required for evaporation and drying. Many operators in these industries lose heat in emissions from their boiler stacks or cooling towers. Recycling of these gases has the two-fold benefit of heat recovery and the reduction of harmful pollutants being released into the atmosphere. Heat is also lost in flash steam from condensate tanks and hot wells.
Process Optimization for Waste Heat Reduction
One of the most important steps towards achieving process optimization is the identification of areas in the plant that represent significant heat sources or heat sinks. This is usually done by analyzing process flow diagrams and conducting heat and material (H&M) balances.
H&M balances are a traditional method used by process engineers to determine the required flow rates of both product and utility streams throughout the process when operating at the specified temperatures. This procedure can be done for the overall process or for individual unit operations. The outcome of this exercise will identify those areas which are either heat sinks or sources and pinpoint opportunities for waste heat recovery.
Designing Your Plant for Heat Recovery
Through process optimization, engineers are able to match heat sources with heat sinks for potential heat recovery. For instance, the waste heat from a boiler stack can be used to reheat crude oil feed to a fractionation tower.
Once sources for recovery have been identified, the plant can be modified by the installation of suitable equipment to recover heat. A shell and tube heat exchanger is commonly used for this duty. Generally, the larger the tube surface area in a heat exchanger, the greater the amount of heat transferred. However, heat exchangers should be sized to maintain an optimum balance between efficiency and cost.