Case Study: Chicago

More Power & Flexibility Lead to Profits at a Cogen Plant in PJM

Project Summary

In 2014, Powerphase installed a Turbophase system consisting of two Turbophase modules, at a cogeneration plant in the U.S. The Morris Cogen plant is a 177 MW combined-cycle gas facility located within the Equistar Chemicals petrochemical plant in Morris, IL. The Morris plant has a single pressure steam turbine (ST) (625 psig/750°F) rated at 57 MW, and three GE MS6001B, PG6561 gas turbines (GTs) upgraded to DLN1 combustion systems each with a HRSG. Equistar buys all the plant’s steam and part of the electricity. The Pennsylvania-Jersey-Maryland (PJM) West market buys the rest of the electricity. PJM needs peaking capacity, having had forced outages during the 2014 Polar Vortex.

New gas-fired capacity is being built. However, these systems take time to permit, build, and commission. However, Turbophase modules can help fill the gap today and beyond. The Turbophase system can boost capacity to existing GT plants, adding new capacity quickly because they take only a few months to install and commission.

The Morris Co-gen Turbophase system was tested in Summer 2014 and has been in operation since then. The Powerphase team has collaborated with the plant owner over the last 3 years to ensure optimal performance and the latest Turbophase system.

Today’s Turbophase system has a new, lower pressure ratio compressor that produces 10% more air flow and thus provides more power to air production for the GT. The system boosts power plant output by 7.3 MW within 1 minute, allowing the Morris plant to sell additional capacity to PJM during peak demand events.

Besides proving fast response that meets PJM requirements for peak demand events, Powerphase also ensured the Turbophase system would protect itself and the GT if it were tripped. Fail safes built into the Turbophase system protect not just the plant and its equipment but the personnel as well. All in all, the Turbophase system is a safe and economical option to boost GT plant performance.

Market Background

The Morris plant sells power to Equistar Chemicals and the nearby regional transmission operator (RTO), PJM. It could make additional revenue if it could boost its generating capacity on demand to sell power to PJM’s ancillary market. A peaking plant that can respond within 10 minutes to a PJM peaking event will be paid for providing the ancillary service, whether it is operating as a synchronized reserve, fast grid regulation, or black start service. PJM was at the top of its peaking capacity, failing to meet 36 GW of peak demand during the 2014 Polar Vortex so that customers were without power during extremely cold temperatures.

Peaking capacity can be developed two ways. One is to build more gas-fired combined cycle turbine, aeroderivative engine, or diesel-powered plants, which can be started, synchronized, and at maximum load in less than the PJM 10-minute requirement to supply grid regulation power. The other is to add Turbophase systems to existing gas turbine plants to boost their response time. Testing results from the Morris plant shows that a Turbophase module reduces grid response time, which may allow the plant to provide ancillary services in a higher paying grid response category.

By The Numbers

Project Details
Engine Type GE 6B
Configuration Combined Cycle
Megawatts as Installed 3.65 MW Per CT
Megawatts Potential 4.25 MW Per CT
PJM Capacity Payment Yes
PJM Reg. Score Imp. Yes

How It Works

Gas Turbines draw ambient air into their axial flow compressor, increasing the temperature and pressure of the air. The air then flows into the combustor where fuel is added proportionate to the amount of air mass flow and the mixture is ignited. This high-energy gas now expands through the turbine stages, creating mechanical torque to drive the gas turbine’s compressor and the net torque drives the generator producing electrical power.

The challenge faced by all gas turbines is that as ambient temperature or elevation rises, the density of the air naturally decreases, reducing the mass flow into the gas turbine. This reduced mass flow results in reducing the fuel flow proportionately to hold turbine inlet temperatures constant. This results in lower output.

Turbophase restores the mass flow that is naturally missing by injecting air into the compressor discharge. The gas turbine control system reacts naturally and adds a proportionate amount of fuel to account for the increase air mass flow, resulting in constant combustion and turbine inlet temperatures. The increased mass flow through the turbine section increases the mechanical torque to the compressor and generator.

Turbophase is a packaged system with a reciprocating engine driving a multi-stage, intercooled centrifugal air compressor. Air is drawn into system to ventilate the system and provide air to the compressor. The compressor air filtration system mirrors the air quality of the gas turbine and then is compressed by the first stage of the air compressor and then cooled. The inter-cooled process is repeated through four or five stages, depending on the desired pressure, resulting in less power required per pound of air compressed compared to the axial compressor in a gas turbine. After the final stage of compression, the compressed air flows directly into the recuperator, a heat exchanger which transfers the waste heat of the reciprocating engine exhaust into the compressed air. The Turbophase module can generate air at gas turbine compressor discharge pressure and temperature 30 to 40% more efficiently than the gas turbine itself.

A Turbophase system can have several modules and each module produces a certain mass flow of pressurized hot air. Each module is factory acceptance tested to ensure quality including correct air pressure and temperature prior to shipment to the power plant site. Depending on the size of the gas turbine, and the requirements of the power plant, a Turbophase system may have 1 module or more than 10 modules. Each module is approximately 32 feet long by 8 feet wide by 18 feet tall at its highest point. A typical Turbophase installation requires no unplanned outage at the plant.


Customer Challenges

PJM needs additional peaking capacity and fast peaking plant response for seasonal peaks, which are exacerbated by extreme weather events. In January 2014, PJM reported it “really exhausted every megawatt we had on the system” to meet record demand due to the Polar Vortex. The RTO needs additional peaking capacity, fast.

A Turbophase module is a less expensive investment than a new peaking gas turbine. It can be deployed much faster than a peaking plant because it can be added to an existing plant. Therefore, there is no need for design, permitting, commissioning, and interconnection to the grid as there would be with a new plant. For plant owners in a capacity constrained market like PJM, this boost can enable them to quickly enter the valuable ancillary services market to provide synchronized reserve, fast grid regulation, and/or black start service. In fact, ancillary service payments often justify the cost of constructing a simple cycle peaking plant.

On an operating gas turbine, Turbophase can ramp to full load in less than 60 seconds, and from part load to full load in less than 10 seconds. An existing simple cycle or combined cycle GT plant can add as much as 10-20% more power to the grid in seconds, depending on plant configuration, addressing the quick-start and fast-response needs of the modern grid. This functionality will certainly be of interest to grid dispatchers anxious to quickly backfill lost capacity during a system emergency or to quickly respond to the intermittency of renewable resources.

Turbophase is also a better alternative to centrifugal chillers and coils that are often used to increase GT power output during warm weather. It injects clean compressed air upstream of the combustor, which is preferable to wet compression resulting from the use of evaporative coolers. Turbophase is less expensive and has higher operating availability than a chiller. Chillers draw power from the GT to refrigerate cooling water for 16 to 18 hours a day so is only available 6 hours a day while parasitically reducing electricity output from the turbine. A Turbophase module is available 24 hours a day, and it allows a GT to operate at its rated capacity irrespective of the ambient conditions or altitude. Moreover, Turbophase is easily adapted to many systems because it produces compressed air at 300 psi, so that it can be used on most E-, F-, and G-class GTs and aeroderivative engines, assuming there is a suitable open port on the casing at the compressor discharge.


Project Milestones

The Turbophase system was installed and tested in 2014. Initial testing showed that the system boosted the GT output by 2.7 MW and the ST output by 0.3 MW. The tests also revealed that the GTs were not firing at their design firing temperature. The central control room equipment miscalculated the baseload firing temperature (TTRF1) as 2,070°F (1,132°C) because the GT Mark V control constants were set incorrectly. The Turbophase engineering team analyzed the engine performance data and determined that the true firing temperature was 2,004°F (1,096°C). The error in control room estimated firing temperature was confirmed by a 3rd party engineering company hired by the plant owner. The combustion and turbine hardware installed in the gas turbine can operate at a firing temperature of 2,042°F (1,117°C). The Turbophase team worked with the plant management and a 3rd party engineering group to update the GT exhaust control curves, to correct the Mark V TTRF1 calculation and set the GTs to the correct firing temperature of 2042°F (1,117°C).

After the constant firing temperature bias was applied and the firing temperature calculation corrected, the Morris plant’s Turbophase system was retested. With the corrections, each Turbophase module boosted GT performance by 3.2 MW and ST performance by 0.45 MW, for a total plant performance boost of 7.3 MW.

Since the initial 2014 installation and testing at the Morris plant, Powerphase engineers have improved Turbophase efficiency. Today, Turbophase systems achieve 10% additional flow by optimizing the compressor for a lower pressure ratio used by the B/E class gas turbines. The Morris compressor was originally optimized to operate on an F class gas turbine with its higher pressure ratio. The Powerphase team updated the Morris plant’s Turbophase system with a new compressor that has a lower inertial mass. The compressor has lighter impellers and better bearings, which allows more power to be used in producing air.

The Turbophase system is a top safety performer. Besides proving fast response that meets PJM requirements for peak demand events, Powerphase also ensured the Turbophase system would continue performing if air supply were interrupted, the air injection line to the GT were highly pressurized, and that it would protect itself and the GT if it were tripped. Safety tests showed that if the GT or one of the Turbophase module trips, the fail safes built into the Turbophase system will protect the plant’s equipment, Turbophase module, and the GT. The Turbophase fail safes were tested by tripping one Turbophase module while injecting air into the GT. All in all, the Turbophase system is a safe and economical option for the plant and its personnel.


Next Steps

Following on the successful demonstration of Turbophase modules on the GT, SEC could expect a standard installation of five to seven Turbophase modules to provide significant benefits. At the as-found conditions of the GT, each Turbophase module adds 4.25 MW at 8,650 BTU/kWh to the GT, for a total of 8.5 MW at 8,100 heat rate. Performance calculations show the heat rate closer to 8,000 BTU/kWh. By extrapolating the Turbophase output from the current firing temperature of 2,370F to the design point of 2,420F, the output increases to 4.5 MW at 7,600 BTU/kWh heat rate.

An installation of 5 modules would result in an output increase of 22.5 MW. At 122°F (50°C) ambient air temperature, this results in a 19% output increase and 3.5% heat rate improvement. An installation of 7 modules would result in an output increase of 31.5 MW. At 122°F (50°C) ambient temperature, this results in a 26% output increase and a 5% heat rate improvement.

Overall, during Summer 2015 operations, the Turbophase modules were over 97 percent available and enhanced the GT output by additional 3.2 GWh. Turbophase module availability was mainly impacted by diesel power supply, water supply, and Turbophase module cooldown time after operations that limited it to a 12-hour shift. There were also failed Turbophase module starts that were solved with a new control upgrade and a lower ramp rate; Turbophase module trips caused by pressure sensor malfunction which was resolved by replacing it, and high gas temperature which was addressed by replacing the gas solenoid valve with a pneumatic valve.

In addition to conducting a successful Turbophase module demonstration, Powerphase also helped SEC identify additional operating and equipment inefficiencies. The Powerphase team discovered that the GT was heavily eroded with significant gaps between stationary and rotating parts which significantly decrease efficiency and output of the gas turbine. They alerted SEC plant personnel, so that the SEC could decide whether to replace the part. The Powerphase team also found that the GT was not operating at the designed firing temperature of 2420°F. They estimated that the GT was operating at firing temperature of 2370°F, confirmed by site operations and validated with a ThermoFlow model matching the site operating conditions. Operating at a lower temperature reduced overall efficiency, including air intake, such that if the GT was firing at its designed firing temperature, the Turbophase modules would have boosted the GT power output by an additional 0.2 MW.


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