Performance and Efficiency Enhancements of Gas Engine Generators
by Starlight Generator dieselgeneratortech2.4.4
Performance and Efficiency Enhancements
2.4.4.1 Brake Mean
Effective Pressure (BMEP) and Engine Speed Engine power is related to engine
speed and the BMEP during the power stroke. BMEP, as described above, can be
regarded as an “average” cylinder pressure on the piston during the power
stroke, and is a measure of the effectiveness of engine power output or
mechanical efficiency. Engine manufacturers often include BMEP values in their
product specifications. Typical BMEP values are as high as 320 psig for large
natural gas engines and 350 psig for diesel engines. Corresponding peak
combustion pressures are about 2,400 psig and 2,600 psig respectively. High
BMEP levels increase power output, improve efficiency, and result in lower
capital costs ($/kW).
BMEP can be increased by
raising combustion cylinder air pressure through increased turbocharging, improved
aftercooling, and reduced pressure losses through improved air passage design.
These factors all increase air charge density and raise peak combustion
pressures, translating into higher BMEP levels.
However, higher BMEP
increases thermal and pneumatic stresses within the engine, and proper design and
testing is required to ensure continued engine durability and reliability.
2.4.4.2
Turbocharging
Essentially all modern
engines above 300 kW are turbocharged to achieve higher power densities. A turbocharger
is basically a turbine-driven intake air compressor. The hot, high velocity
exhaust gases leaving the engine cylinders power the turbine. Very large
engines typically are equipped with two turbochargers. On a carbureted engine,
turbocharging forces more air and fuel into the cylinders, which increases the
engine output. On a fuel injected engine, the mass of fuel injected must be
increased in proportion to the increased air input. Cylinder pressure and
temperature normally increase as a result of turbocharging, increasing the
tendency for detonation for both spark ignition and dual fuel engines and requiring
a careful balance between compression ratio and turbocharger boost level.
Turbochargers normally boost inlet air pressure on a 3:1 to 4:1 ratio. A wide
range of turbocharger designs and models are used. Heat exchangers (called
aftercoolers or intercoolers) are normally used on the discharge air from the
turbocharger to keep the temperature of the air to the engine under a specified
limit.
Intercooling on forced
induction engines improves volumetric efficiency by increasing the density of intake
air to the engine (i.e. cold air charge from intercooling provides denser air
for combustion thus allowing more fuel and air to be combusted per engine
stroke increasing the output of the engine).
2.4.5
Capital Costs
This section provides
typical study estimates for the installed cost of natural gas spark-ignited, reciprocating
engine-driven generators in CHP applications. Capital costs (equipment and
installation) are estimated for the five typical engine genset systems ranging
from 100 kW to 9 MW. These are “typical” budgetary price levels; it should also
be noted that installed costs can vary significantly depending on the scope of
the plant equipment, geographical area, competitive market conditions, special
site requirements, emissions control requirements, prevailing labor rates, and
whether the system is a new or retrofit application.
The basic generator
package consists of the engine connected directly to a generator without a
gearbox.
In countries where 60 Hz
power is required, the genset operates at multiples of 60 – typically 1800 rpm for
smaller engines, and 900 or 720 or 514 rpm for the large engines. In areas
where 50 Hz power is used such as Europe and Japan, the engines run at speeds
that are multiples of 50 – typically 1500 rpm for the small engines. In Table
2-4, System 4 is based on a German design, and operates at 1,500 rpm and produces
60 Hz power through a gearbox. The smaller engines are skid mounted with a
basic control system, fuel system, radiator, fan, and starting system. Some
smaller packages come with an enclosure, integrated heat recovery system, and
basic electric paralleling equipment. The cost of the basic engine genset
package plus the costs for added systems needed for the particular application
comprise the total equipment cost. The total plant cost consists of total
equipment cost plus installation labor and are about 2,400 psig and 2,600 psig
respectively. High BMEP levels increase power output, improve efficiency, and
result in lower capital costs ($/kW).
BMEP can be increased by
raising combustion cylinder air pressure through increased turbocharging, improved
aftercooling, and reduced pressure losses through improved air passage design.
These factors all increase air charge density and raise peak combustion
pressures, translating into higher BMEP levels.
However, higher BMEP
increases thermal and pneumatic stresses within the engine, and proper design and
testing is required to ensure continued engine durability and reliability.
2.4.4.2
Turbocharging
Essentially all modern
engines above 300 kW are turbocharged to achieve higher power densities. A turbocharger
is basically a turbine-driven intake air compressor. The hot, high velocity
exhaust gases leaving the engine cylinders power the turbine. Very large
engines typically are equipped with two turbochargers. On a carbureted engine,
turbocharging forces more air and fuel into the cylinders, which increases the
engine output. On a fuel injected engine, the mass of fuel injected must be
increased in proportion to the increased air input. Cylinder pressure and
temperature normally increase as a result of turbocharging, increasing the
tendency for detonation for both spark ignition and dual fuel engines and requiring
a careful balance between compression ratio and turbocharger boost level.
Turbochargers normally boost inlet air pressure on a 3:1 to 4:1 ratio. A wide
range of turbocharger designs and models are used. Heat exchangers (called
aftercoolers or intercoolers) are normally used on the discharge air from the
turbocharger to keep the temperature of the air to the engine under a specified
limit.
Intercooling on forced
induction engines improves volumetric efficiency by increasing the density of intake
air to the engine (i.e. cold air charge from intercooling provides denser air
for combustion thus allowing more fuel and air to be combusted per engine
stroke increasing the output of the engine).
2.4.5
Capital Costs
This section provides
typical study estimates for the installed cost of natural gas spark-ignited, reciprocating
engine-driven generators in CHP applications. Capital costs (equipment and
installation) are estimated for the five typical engine genset systems ranging
from 100 kW to 9 MW. These are “typical” budgetary price levels; it should also
be noted that installed costs can vary significantly depending on the scope of
the plant equipment, geographical area, competitive market conditions, special
site requirements, emissions control requirements, prevailing labor rates, and
whether the system is a new or retrofit application.
The basic generator
package consists of the engine connected directly to a generator without a
gearbox.
In countries where 60 Hz
power is required, the genset operates at multiples of 60 – typically 1800 rpm for
smaller engines, and 900 or 720 or 514 rpm for the large engines. In areas
where 50 Hz power is used such as Europe and Japan, the engines run at speeds
that are multiples of 50 – typically 1500 rpm for the small engines. In Table
2-4, System 4 is based on a German design, and operates at 1,500 rpm and produces
60 Hz power through a gearbox. The smaller engines are skid mounted with a
basic control system, fuel system, radiator, fan, and starting system. Some
smaller packages come with an enclosure, integrated heat recovery system, and
basic electric paralleling equipment. The cost of the basic engine genset
package plus the costs for added systems needed for the particular application
comprise the total equipment cost. The total plant cost consists of total
equipment cost plus installation labor and materials (including site work),
engineering, project management (including licensing, insurance, commissioning
and startup), and financial carrying costs during the 4 to 18 month
construction period.
All engines are in low
NOx configuration. System 1, a stoichiometric (rich burn) engine, uses a
three-way catalyst to reduce emissions to their final level. The other systems
are all lean burn engines and are shown with a SCR, CO catalyst, and continuous
emissions monitoring system (CEMS) that are required in environmentally
sensitive areas such as Southern California and the Northeastern U.S.
Table 2-4 provides cost
estimates for combined heat and power applications based on a single unit engine.
The CHP system is assumed to produce hot water, although the multi-megawatt
size engines are capable of producing low-pressure steam. The heat recovery
equipment consists of the exhaust economizer that extracts heat from the
exhaust system, process heat exchanger for extracting heat from the engine
jacket coolant, circulation pump, control system, and piping. These cost
estimates include interconnection and paralleling. The package costs are
intended to reflect a generic representation of popular engines in each size
category. The interconnection/electrical costs reflect the costs of paralleling
a synchronous generator for the larger systems. The 100 kW system uses an
inverter based generator that has been pre-certified for interconnection in
most areas. Labor/materials represent the labor cost for the civil, mechanical,
and electrical work as well as materials such as ductwork, piping, and wiring.
Project and construction
management also includes general contractor markup and bonding, and performance
guarantees. Contingency is assumed to be 5 percent of the total equipment cost
in all cases. Cost estimates for multiple unit installations have lower unit
costs than single unit installations.
Sponsor Ads
Created on Apr 23rd 2019 22:05. Viewed 261 times.