10311Quality of Recoverable Heat

The thermal requirements of the end user may dictate the feasibility of a CHP system or the selection of the prime mover. Gas turbines offer the highest quality heat that is often used to generate power in a steam turbine. Gas turbines reject heat almost exclusively in their exhaust gas streams. The high temperature of this exhaust can be used to generate high-pressure steam or lower-temperature applications such as low-pressure steam or hot water. Larger gas turbines (typically above 25 MW) are frequently used in combined cycles where high-pressure steam is produced in the HRSG and is used in a steam turbine to generate additional electricity. The high levels of oxygen present in the exhaust stream allow for supplemental fuel addition to generate additional steam at high efficiency.

Some of the developing fuel cell technologies, including MCFC and SOFC, will also provide high quality rejected heat comparable to a gas turbine. Reciprocating engines and the commercially available PAFC produce a lower grade of rejected heat. Heating applications that require low-pressure steam (15 psig) or hot water are most suitable, although the exhaust from a reciprocating engine can generate steam up to 100 psig.

Reciprocating engines typically have higher efficiency than most gas turbines in the same output range and are a good fit where the thermal load is low relative to electric demand. Reciprocating engines can produce low- and high-pressure steam from their exhaust gas, although low-pressure steam or hot water is generally specified. Jacket water temperatures are typically limited to 210°F so that jacket heat is usually recovered in the form of hot water. All the jacket heat can be recovered if there is sufficient demand; however, only 40 to 60% of the exhaust heat can be recovered to prevent condensation of corrosive exhaust products in the stack that will limit equipment life.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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