Cogeneration CHP, Equipment, Strategic Development

Bigger than nuclear

Figure 1 shows RMI’s findings about the installed capacity of worldwide micropower in 2004, Figure 2 the annual output. Also shown are the respective industries’ approximate projections to 2010. These are imprecise but qualitatively clear. All data shown are net of increases or decreases in rated capacity and of re- and decommissioned units.

Output lags capacity by three years as CHP has a higher average capacity factor than wind and solar, although some small hydro projects and most geothermal and biomass generation projects also have high capacity factors. Precise data on the fuel mix of CHP are not available, but WADE estimates it at 60%–70% gas-fired. This implies a CHP carbon intensity probably no more than half the global average for centralized fossil-fuelled generation, which is coal-dominated, with a normal range of around 30%–80% depending on relative efficiencies and fuels.

65% of micropower’s 2004 capacity and 77% of its output was fossil-fuelled CHP; the rest, diverse renewable sources

LOW OR NO-CARBON EMISSIONS

Since the renewable sources shown have zero direct carbon emissions, as does nuclear power if its enrichment energy and any decommissioning or wastedisposal energy are neglected, all the sources of electricity shown in Figures 1 and 2 are low- or no-carbon emitters.

Nuclear power’s global capacity and output are both graphed for comparison. Fossil-fuelled, non-CHP generation is several times larger. Micropower’s greater market success compared with nuclear power is all the more impressive because nuclear has been heavily promoted and subsidized by nearly all host governments. In the US, for example, it received 24 times more federal subsidies per kWh in 1985 than did non-hydroelectric renewables.1 In nuclear’s first 15 years of industrial development it was about 30 times more heavily subsidized per kWh than all renewables.2 Moreover, micropower in many countries, including most of the US, is often barred from grid interconnection, on fair terms or completely, while centralized plants are not. Cost comparisons typically burden micropower with both grid expansion and firming or backup costs (which are often exaggerated) while the corresponding costs of centralized plants, such as reserve margin, are typically socialized as normal overheads of the electricity enterprise. It seems inescapable that fair competition at honest prices would favour micropower over centralized plants even more than the market has been doing lately.

Maintenance options for gas turbines

The availability of the gas turbine is crucial to the performance of a turbine-based cogeneration plant, and availability is a function of good, well-planned maintenance, writes Simon Raymond. A long-term service agreement, which transfers some financial risk to the service provider, can be the best option for the care of turbines of high capital cost.

Owning and operating a gas turbine is an expensive business. The principle of how a gas turbine works is simplicity itself, but putting that into practice requires mechanically complex pieces of equipment built with high-grade materials and a host of supporting systems that need to work in harmony.


Figure 1. The goals that a gas turbine operator and maintenance provider strive for

The inherent design of a gas turbine is naturally a major factor in how reliably it performs in service, but of at least equal importance is how the equipment is looked after, or maintained, while it is in service. Having invested a large amount of capital in a gas turbine power plant with all its ancillary equipment, the owner will want to maximize the return on that investment by having that power plant running at a high level of reliability while keeping running costs to a minimum.

The power advantages of a gas turbine over, for example, a like-sized diesel engine are offset to some extent by its need for routine maintenance and its relatively high servicing costs. Gas turbines do not forgive poor maintenance. It will cause them to stop functioning soon. The repair costs of a poorly maintained turbine can be frightening, to say nothing of the disruption to the owner’s operation. If a satisfactory balance between maintenance and cost can be found, then extraordinary reliability is achievable while preserving the owner’s profitability, as Figure 1 shows. But how is this maintenance carried out, and what maintenance philosophies exist?

A gas turbine’s power advantages are offset to some extent by its need for routine maintenance and its high servicing costs 

The owner of a gas turbine power plant is not generally in the business of gas turbines so has neither the ability nor desire to perform the maintenance themselves. Even though some car owners prefer to service their cars themselves, the majority prefer to leave the job to a specialist. Yet if a car were bought for many millions of dollars, it is extremely unlikely that an owner would be carrying out the maintenance and servicing!