Page 293 - Sustainable On-Site CHP Systems Design, Construction, and Operations

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chilled water. Absorption chillers generally use large volumes of steam at relatively low
pressures to provide a constant supply of chilled water.
In many cases, as the building heat loads decrease, the cooling loads increase. These
are ideal conditions, which, for example, will allow the plant operator to shift the flow
of steam from the building heat to steam-driven centrifugal or absorption chillers, or to
steam-assisted power auxiliaries, for example, fans and pumps where installed. There
are also cases where, during a hot humid afternoon, the electric load is at a maximum
level and all most of the steam would be better directed to the STG to provide more
electricity production.
Computer Data Logs
Microprocessor-based monitoring and control systems are normally distributed
throughout the plant. They are designed and programmed to provide plant control
through set points as well as process and safety limits for all major pieces of equipment
in the plant. Computers with graphic displays sometimes called HMI. The HMI takes
data from the control system and provides process information and points of control for
the plant operator. The HMI also provides an opportunity for the plant operators or
management to produce both historic data and real-time data.
Data logs can be generated in various formats such as graphs, bar charts, and
tables. The information about plant performance and efficiency can be gathered in the
computer and displayed in a manner that is easily understood. The plant operators
should be able to equate their decisions and actions while operating the plant to the
outcomes displayed, and be able to make adjustments and see the results over a short
period of time.

Plant Maintenance

CTG
Most maintenance on a CTG or reciprocating engine requires a shutdown and the work
often requires the expertise of factory-trained and experienced mechanics. The plant
operator has a responsibility to be aware of any changes in plant readings. The operator
must be on the alert for any unusual operating conditions that may be indicated by
changes in vibration or noise.
One of the most important responsibilities of the plant operator is to inspect and
maintain the integrity of the lube oil system. The condition of the lube oil can be
visually checked for color and flow and level in the storage tank. Lube oil tempera-
ture and differential pressure at the filters should be monitored and alarmed in the
control system.
Keeping a CTG clean will provide the best opportunity to maximize its efficiency
over time. The inlet filters must be monitored and changed as often as necessary to
prevent excessive pressure drops which degrade CTG performance. Even the best fil-
ters will not prevent a CTG from getting dirty. Some turbines have an option to water
wash while the turbine is running rather than requiring a shutdown.
HRSG
The heat recovery steam generator is basically an unfired water-tube boiler. The HRSG
is specifically designed to generate saturated steam from the CTG engine exhaust gas.