Page 195 - Sustainable On-Site CHP Systems Design, Construction, and Operations

168 De s i g n

a number of design issues and challenges that must be addressed and solved as part of
the engineering design effort. CHP systems typically include many components that
the engineering design team must understand. The engineering design team must have
knowledge of the various types, uses, installation requirements, and maintenance
requirements for CHP systems. As discussed in Chaps. 3 and 4, some of the major CHP
components include prime movers; heat recovery systems; HRSGs; heat exchangers;
pumping systems; thermal chillers; steam turbines; applicable, thermally regenerated
desiccant air-conditioning systems; emissions control and monitoring systems; cooling
towers; radiators; fuel systems (including fuel storage systems); lube oil systems
(including oil and waste oil storage systems); steam, condensate, and feedwater
systems; hot water systems; chilled water systems; condenser water systems; and building
or enclosure heating, ventilating, and air-conditioning (HVAC) equipment.
The engineering team must be able to calculate heat balances, size and select equip-
ment, size piping and ductwork, calculate water, air, and exhaust pressure drops,
estimate energy use and cost, as well as develop the proper generator interconnections
and electrical protection safeguards.
Of course, as outlined above and discussed in other chapters, the proposed CHP
system must meet all the codes, regulations, and standards for the project location. The
engineering team will have a good idea of the required codes and standards from previous
design efforts and from the code and standards review conducted as described previ-
ously. Further, when the actual design effort begins, the maximum emissions levels
allowed by the expected permit to operate, the expected raw prime mover emissions
levels, and the required emissions reduction equipment must be known, at least con-
ceptually. For example, the air quality agency will require 15 ppm NO , the CTG emits
x
25 ppm NO , and the CHP system will employ selective catalytic reduction (SCR) to
x
reduce NO to below the allowable maximum emissions limit. Given thorough, well-
x
coordinated, construction documents that follow the required codes and standards, the
project should be able to obtain a permit to construct.
As discussed in Chap. 4, the type of prime mover selected to meet the facility’s power
and thermal needs will have a major impact on the amount, quality (temperature and pres-
sure), and type of heat recovery available, as well as have an impact on the type of systems
and materials employed in the CHP design. For example, a combustion turbine generator
(CTG) may have a heat recovery steam generator (HRSG) to produce high-pressure steam,
while an internal combustion (IC) engine may produce hot water from engine cooling and
from exhaust heat recovery. The quality of the recovered heat will, of course, impact the
available thermal-powered chiller options, as double-effect absorption chillers and steam
turbine–driven chillers require high-pressure steam to operate. Additionally, CTGs typi-
cally require high-pressure gas, which usually necessitates the need for gas compressors,
while most IC engine generators can use low-pressure gas and often do not need a gas
compressor. Generally, the larger the CTG, the higher is the required gas pressure.
Also as discussed in this book, complete use of the available recovered waste heat
is paramount to achieving a sustainable CHP system. Therefore, the design must incor-
porate methods to fully use as much of the recovered heat as possible by providing for
a number of thermal uses, such as space heating, space cooling, domestic hot water
production, desiccant dryer systems for dehumidification, swimming pool heat, and
process loads. Where conditions exist when all of the thermal output cannot be used, a
way of rejecting all of the heat is needed (note, full heat rejection capability is typically
also required at least for start-up and testing).