Page 62 - Energize April 2022

TECHNICAL

Gas to power: Reciprocating

gas engines vs. gas turbines for

medium power applications

Developments in power generation, such as microgrids, large hybrid systems, renewable energy
balancing systems and backup systems, all use fuel-based generation plant as components.
Gas is becoming the fuel of choice primarily because of lower CO emissions, increasing availability
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and lower costs. A variety of gas-fuelled generators are available, and the choice of technology
depends on the application.

BY MIKE RYCROFT, ENERGIZE

wo technologies are available in the range covered by applications, less than 100 MW, but plants of over 400 MW
these systems (10 to 100+ MW): gas turbines (GT) and have been delivered. The largest project, over 600 MW, was
Treciprocating gas engines (RGE), the latter technology inaugurated in Jordan in April 2021. 6
benefitting from enjoying recent extensive development, resulting
in increased size and improved efficiency. Applications can include:
Small to medium sized GT running from 1 to 50 MW have • Continuous operation with either fixed load or load following
become available on the market and with single gas engines (varying load)
approaching 20 MW in size, there is considerable overlap between • Cyclic operation such as peak load following in a fixed pattern
the technologies, especially where multi-unit installations are and duration
concerned. The choice of technology will depend on a number of • Generation balancing with intermittent operation in no fixed
factors. pattern but limited duration
Both gas turbines and gas engines have proven themselves • Emergency operation with no fixed pattern or duration
to be valuable in power generation applications. Each technology • Combined heat and power generation
has found favour with users looking for reliable power and • Combined cycle turbine operation
thermal alternatives. Development of RGE capabilities has made
multiple installations a popular choice in the range below 200 MW, Applications in the range considered can be divided into two basic
while small to medium gas turbines offer an increasing range of groups for comparison of characteristics.
applications. • Power only: the system is used for generation of electricity
Both turbines and engines offer the possibility of combined only - this application is associated with the requirement for
heat and power (CHP) production. The high temperature exhaust quick start up, rapid ramping and load following. Load following
gas from turbines can be used to generate high grade steam which is typically used for generation or load balancing, cyclic and
can be used either to drive steam turbines to generate electricity emergency operations.
or provide heat for industrial processes. Lower quality heat • Combined heat and power (CHP): this includes combined cycle
recovered from engine exhaust and cooling systems can be used gas turbines using high grade steam, and combined heat and
for hot water and low-grade steam production. All of this means a power systems using low grade steam or hot water for industrial
strong opportunity for gas-fuelled CHP systems. or district heating usage (usually operated as baseload systems
Gas turbines have traditionally been used for power projects where rapid ramping and quick start is not required.)
1
above 100 MW. But changing market conditions mean that
gas engines can compete at this scale. Previous limits for RGE The importance of modularity
technology were somewhere in the 50 to 70 MW range but now Modularity in power plant design enhances flexibility and
there is evidence that engines are competitive in the range 200 reliability. Traditionally, loads in the multi-MW sector were
MW and above. 2 handled by gas turbines, but multiple gas engine installations
This competitiveness can be attributed to advances in engine are finding increasing application in the range up to 200 MW,
technology, as well as to the achievement of higher efficiencies. especially where operation at partial load and short start-uptimes
Engine technology was previously used only in small-scale is a requirement. Modular installations facilitate maintenance,

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