Two 6.6 MW Reciprocating Engines and 8,500 lbm/h HRSGs

1) Cogeneration

2) Electric Utility

1) Cogeneration

2) Boiler Plant

Table 26-12 Three Plant Options.

Table 26-12 Three Plant Options.

Cogeneration System Plant Configuration: Case GT-1

Equipment Configuration

This cogeneration plant consists of three gas turbine generator sets, associated heat recovery boilers, electrical switchgear, and auxiliary equipment from Solar Turbines. Total plant capacity includes 14.3 MW of electricity at 60°F (15.6°C) outside temperature and 74,100 lbm/h (33,611 kg/h) of 150 psig (11.4 bar) steam. This configuration does not include supplemental firing of HRSGs.

The plant will be controlled to track the facility's electrical demand and produce as much of that demand as the plant can provide. The simulation will start one gas turbine as soon as the electrical load exceeds the minimum operating level for one turbine (50% of capacity) and will start additional turbines as the load exceeds the capacity of the operating turbines. The simulation assumes that all operating engines share the total load equally.

Cogenerated steam production roughly tracks electrical production, resulting in the need to have standby steam-generating capacity. For this reason, the simulation assumes that one of the existing Cleaver-Brooks boilers will operate to maintain temperature for all hours of the year.

Maintenance Requirements

Solar Turbines reached agreement with the facility to offer a five year extended service program for the plant that will cover all scheduled and emergency maintenance and repairs. The cost for the program is $3.50 per MWh generated, with a guarantee of 95% availability for each of the turbines. This program includes eight preventive maintenance visits per turbine per year and unlimited trouble calls. Scheduled maintenance includes a minor service every six month period requiring two to three days of outage per turbine and an annual major overhaul requiring three to five days of downtime per turbine.

The operations simulation has accounted for these scheduled service intervals by making one turbine unavailable for these periods. In order to minimize the impact of this work on the operating cost savings, it was assumed that this work will be scheduled during the July plant shutdown and during minimum load periods in January.

Based on the above unit cost for the maintenance program and the projected total power generation of 98,616 MWh, the annual maintenance cost to the facility for this plant was estimated as:

In addition to this figure, the following two maintenance costs were applied to each year of GT-1 system operation:

1. Maintenance of boilers, steam system, and related equipment totals $50,000 per year.

2. Four operators for 24 hour per day coverage, at

$70,000 each, totals $280,000 per year.

Note that a standalone plant would require more than four operators to provide 24 hour operating coverage. In this case, this study considers the net staff requirement increase over existing boiler plant staff. This assumes that there will be overlap in coverage and responsibilities between boiler plant operations and cogeneration plant operations, and is consistent with the staffing plan prepared by the facility.

Plant Performance

Solar Turbines provided plant operations and performance data. The power output from a gas turbine is highly dependent upon the temperature of the combustion air. For this reason, the performance of the plant has been modeled using two independent variables: outdoor air temperature and load level. For a given outdoor air temperature, the plant will have a capacity three times that of a single gas turbine unit.

Steam generation capacity is a function of exhaust flow, exhaust temperature, and steam pressure. Because the plant controller will operate the gas turbine to generate as much power as the facility needs, there may be periods when the steam capacity of the heat recovery boilers exceeds the total boiler load. Under these conditions, exhaust gas would be diverted around the heat recovery boiler, thereby eliminating the need to vent steam to atmosphere. The simulation is capable of detecting and allowing for this condition.

Table 26-13 shows a subset of the performance data for this cogeneration plant configuration, including electrical and steam production, as well as fuel consumption values for the plant as a function of ambient temperature. These values are used by the operations simulation discussed below.

Project Cost

The study team developed a project cost estimate to implement this cogeneration configuration, including the cogeneration equipment described above, extension of the existing boiler plant building structure over the cogenera-tion system, construction, and system startup. The total cost to complete this project was estimated at $13,950,000, as summarized in Table 26-14.

Cogeneration System Plant Configuration: Case RE-1

Equipment Configuration

This system is based on the installation of two gas-fired reciprocating engine-generators, heat recovery boilers, hot water heat exchangers, electrical switchgear, and auxiliary equipment from Coltec Industries/Fairbanks Morse Engine Division. Total plant capacity includes 13.06 MW of electricity, 13,800 lbm/h (6,260 kg/h) of 135 psig (10.3 bar) steam, and 21.8 MMBtu/h (22,988 MJ/h) of hot water at 180°F (82°C).

Switchgear will be installed to control the engine-generators, with capacity control to limit electrical production to the facility's electrical demand. The generators produce power at 13.8 kV, so that this can be tied directly into the existing facility switchgear without the need for a transformer.

Thermal energy from the engines will be used to offset steam heat in two areas. First, a new heat exchanger will be installed to use the hot water to preheat boiler makeup water from approximately 70°F (21°C) up to 170°F (77°C). For this analysis, the magnitude of this load was estimated by assuming this temperature change on a flow equivalent to 25% of the steam flow (corresponding to a makeup rate of 25%). Any additional heating requirements will be met by a combination of the existing deaerating feedwater heater and the economizer feedwater heater.

The other thermal load for hot water from the engines is process hot water load within the manufacturing plant. This analysis was based on a load of 4 MMBtu/h (4,200 MJ/h) for heating reject process water from an existing holding tank from an initial temperature of 120°F (49°C) up to approximately 170°F (77°C). Currently,



Engine Generators


Electrical Switchgear




Design/Construction Services


Overhead and Profit






Table 26-14 Capital Cost Summary for Gas Turbine Cogeneration System.

Table 26-14 Capital Cost Summary for Gas Turbine Cogeneration System.

this water is heated to 170°F (77°C) by steam heat exchangers. Included in the cost estimate is a hot water piping system consisting of 1,500 ft (457 m) of insulated 6 in. (15 cm) piping, with all associated heat exchangers, pumps, controls, and miscellaneous equipment. During any period when the process load is insufficient to provide proper heat rejection for the hot water loop, two waste heat radiators for each engine will maintain return water temperature within acceptable limits.

Maintenance Requirements

Coltec Industries estimated the total scheduled maintenance cost of this plant at $2.90 per MWh. This price was developed assuming the plant operates 8,000 hours per year at 100% load, and includes a breakdown of 30% parts and 70% labor. Additional operating costs include lube oil consumption, estimated at $0.32 per MWh. Based on the simulation projections of 99,312 MWh per year, annual maintenance cost was estimated as follows:

Based on the facility's plan to hire a staff of four

Ambient Temp °F

Electric Capacity

Fuel Rate (MMBtu/MWh)

Steam Capacity (Mlb/MWh)




Load Level

Load Level

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