Heat recovery in the gas compression industry
Background
Natural gas transmission grids use primarily gas turbines and reciprocating engines to move natural gas from a central source to homes and businesses throughout the world. These turbines and engines are typically just like the power generating versions, however turn a mechanical drive compressor to create pressure in the gas pipeline as opposed to turning a generator to create electricity. Just like with power generating applications, these engines and turbines produce a substantial amount of heat as they operate.
The opportunity
To give a sense of the quantity of compressor stations in the world, an estimated 5,400 reciprocating engines and 1,000 gas turbines operate on compression stations in the US alone.
The (US) natural gas pipeline network relies on more than 1,200 compressor stations to maintain a continuous flow of natural gas between supply areas and delivery to local distribution, municipal, industrial and electric generation customers. Compressor stations are usually situated between 50 to 150 miles apart along the length of a pipeline system and are typically designed to operate on an unattended and non-stop basis. (INGAA)
The gas turbines or reciprocating engines operate on the natural gas that they are moving in the pipeline, and the stations are typically in remote areas. As such, it is less common for there to be a heat or cooling demand nearby. As such, one of the more common heat recovery applications for gas compressor stations is to turn the heat into electrical power that can be sold to the grid. Within the heat to power applications, it's most common to use an Organic Rankine Cycle (ORC) generator, which does not require makeup water and is flexible with the operation of the gas turbine or engine.
Key factors and considerations
In a heat to electricity application at a gas compression facility, there are 3 key factors that will determine the viability of a project:
- How much heat is available, and therefore how much power can be generated. The exhaust parameters should be on the specification sheet and can be entered into our calculator to determine the quantity of heat available. Most ORC's operate at 10-20% efficiency, which can help you determine the kW of output generated from the kWth of heat available.
- What is the value of the electricity produced. The higher the electricity rate the better. Most projects need about $0.08/kWh and above to make the project economically viable, unless there are some additional incentives available.
- The average number of operating hours for the project. The more the better. INGAA report recommended at least 5,000 operating hours per year for a viable project (out of a total 8,760 hours per year).