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Compression station fuel gas superheating
As natural gas travels along a pipeline it loses pressure due to friction effects. To maintain pressure, compression stations are required at intermittent points along the pipeline. However, the turbine engines used at many of these stations can suffer from liquid dropping out of the fuel gas, which is caused by the Joule-Thomson effect as the side stream of gas supplied to the turbine decreases in pressure.
Superheating the fuel gas before it enters the turbine can eliminate this risk. This process has traditionally been achieved through using either electric or gas fired water bath heaters, which require both maintenance and an external heat source.
| Elsewhere in the compression train, the compressor lube oil system releases unwanted heat into the atmosphere, typically using air-cooled heat exchangers. There is an obvious advantage to using a diffusion-bonded heat exchanger in this application to combine the two tasks of heating the fuel gas and cooling the lube oil, potentially reducing heat losses and operational expenditure significantly. |  |
Other advantages include:
- Heatric's exchangers are highly compact pieces of equipment. In this application their use can reduce space and structural requirements, allowing the exchanger to be installed beneath the compressor.
- The high pressures and temperatures reached by the lube oil are easily accommodated, as diffusion-bonded exchangers can be designed to pressures over 600 bar and to extreme temperatures (cryogenic to 900°C).
- Using diffusion-bonded heat exchangers can significantly improve safety and reduce pressure relief requirements, as they have no failure mode that is analogous to tube rupture in shell and tube exchangers.
- Materials qualified by Heatric include stainless steels, meaning Heatric exchangers can meet the stringent clean fluid requirements for gas turbine lube oil.
- Due to their unique construction and design, diffusion-bonded exchangers are highly reliable, which is essential in this application. Any disruption to the gas supply can have immediate consequences in this industry, leading to angry customers and a potential loss of business.
- They have a high mechanical integrity, lowering the risk of the interstream leakage that can occur when combining two services.
- There is a very low maintenance requirement, making them highly suited to remote applications.
- There may be a reduction in CO2 emissions resulting from the use of diffusion-bonded heat exchangers, as the fuel gas is preheated making the combustion process more efficient. In some regions of the world, a decrease in CO2 tax may be seen as a result.
National Grid Transco is one company who have realised the opportunities diffusion-bonded heat exchangers provide, and have installed them on several of their compression stations in the UK. Twenty five exchangers are currently installed and operating in this application.
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