Page 290 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Operation and Maintenance Services 263

anticipate every situation, a set of guidelines and procedures are written in a manner to
provide operators with a basic understanding of their responsibilities, information needed
to undertake specific tasks, along with some generalities and expected outcomes. In some
cases, the guidelines will change based on seasonal load patterns. The guidelines are
intended to suggest the selection of equipment available to address the load and at the
same time seek to optimize system efficiency wherever possible. In a CHP plant, it is
important that the plant operators have a number of options where the steam or hot water
produced in the heat recovery steam generator (HRSG) or heat recovery hot water heat
exchanger can either be fully used or shifted to when electric loads change.
It is important to allow operators some slack to make decisions based on observed
conditions, but within guidelines established by management, to ensure that the plant
is not allowed to operate in an inefficient manner. Exceptional operators will, at times,
find methods that will result in changes to prescribed written procedures or guidelines.
Such exceptions must be carefully documented and approved by management only
after proven to be repeatable prior to being written as exceptions into the procedures
manual to avoid misuse.

Plant Start-Up

Black Start
In many CHP plants, the power that is produced is distributed in a parallel configura-
tion with the local utility power to meet the facility load. The total load requirement
may exceed the capacity of the CHP plant and the facility must rely on the utility power
to provide the balance of required electric power. It is not uncommon for the utility
power sometimes to go down (i.e., for a blackout to occur) due to an act of nature, an
overload condition, or equipment failure. When this occurs, it is likely that the CTG or
engine-generator will trip off as well due to voltage disruptions. The facility is now
without power or “black.” The plant operators must try to get power back to the facility
as soon as possible. A black start generator is necessary in this situation, or the plant
operators must wait until the utility power is restored. In some facilities, an automated
load-shed program may prevent the generator from tripping on an overload condition
when utility power is suddenly lost.
A diesel engine generator is commonly used for black start. The plant operators
must first open the circuit breaker to the utility supply to “island” the facility (i.e., dis-
connect the facility from the utility power grid). The facility, if large enough should
have a load-shed plan so the CHP plant can always be started in a balanced load condi-
tion. If the breakers are not automated, the plant operators must be instructed to manu-
ally open the breakers to remove load. The black start generator is usually designed to
provide just enough power to the auxiliary loads that are required to support the start
up of the CHP plant. For example, the auxiliary loads should be capable of supporting
the CTG and the associated HRSG under emergency conditions.
In addition to the auxiliary loads, the black start generator provides a voltage and
frequency that the CHP prime mover can read and be synchronized with. Once the
engine is rolling and has completed its warm-up cycle, the plant operator will bring
the engine up to operating RPM and then bring the generator online. The generator
frequency must be synchronized to the line frequency. The plant operator usually has
the option to initiate synchronization with an automated control or in a manual mode. In