Making Power Multitask With CHP/CCHP
Cogeneration and trigeneration: industry experts say the time is ripe—again—for the increased use of these technologies.
By Carol Brzozowski
Cogeneration, or combined heat and power (CHP), uses a heat engine or power station to generate electricity and heat for onsite uses. Trigeneration, or combined cooling, heat, and power (CCHP), is the simultaneous generation of electricity and useful heating and cooling as a result of the combustion of fuel or the action of a solar heat collector.
According to Elite Energy Systems, CHP principles have been around since the late 1800s when Thomas Edison used them to power the world’s first commercial power plant. But as the need for electricity spread to rural parts of the country, government regulations were put in place to promote centralized power plants managed by regional utility companies.
Decentralized sources of energy such as CHP were discouraged, culminating in a law barring non-utilities from selling power. Thirty years ago, CHP once again became a favorable form of energy production after Congress acknowledged large power plants, though a convenient form of electricity production were inefficient in capturing the energy they produce and contributed to air pollution, according to Elite Energy Systems.
Advances in cogeneration and trigeneration technology are pushing the efficiency boundaries of reciprocating engine-generators, adding to the appeal and financial return of engine systems for private and public entities that are used to using large amounts of power for energy, cooling, or heating.
Michael Devine, the gas product marketing manager for Caterpillar’s Electric Power Division, points out in a white paper that cogeneration with gaseous-fueled engine-generators has delivered “substantial benefits for many years” in Europe and North America, where it provides cost-effective electricity and heating in numerous commercial and industrial settings.
In Asia and elsewhere in the developing world, cogeneration provides a steady source of electricity where utility power reliability and quality are inconsistent, while also delivering heat for process industries that help drive economic growth.
These days, cogeneration is receiving a boost through shale gas development, driving North American natural gas prices down to levels not seen since the 1990s. Average wholesale prices fell 31% in 2012, and recent prices have ranged from $3 to $5 per MMBTU (1 million BTUs). This helps enable attractive payback on the front end of cogeneration projects, Devine points out. The long-term outlook is just as favorable, with current predictions for natural gas prices to increase by just 2.1% per year through 2035 against the backdrop of escalating utility electricity prices.
“As a result, a widening variety of cogeneration applications have moved squarely into the mainstream,” says Devine. “Cogeneration today goes well beyond the classical picture of simultaneously generating electricity and hot water or steam.” Today’s usable engine outputs also can include heated air, chilled water produced by absorption chillers, and carbon dioxide (CO2) from purified exhaust.
|Photo: Energy Concepts
A 60-ton HeliChiller solar
Varieties of Configurations in CHP, CCHP
“A single engine-generator can produce two, three, or four useful outputs at once,” says Devine. “With today’s generating technologies, electrical efficiencies up to 45% and total resource efficiencies upwards of 90% are achievable. Cogeneration systems do not necessarily need to operate full-time at full load to be cost-effective; low-cost and low-intensity configurations can bring attractive returns in many settings.”
Lean-burn gas-fueled reciprocating engines are rich sources of heat. Heat that is otherwise wasted can be extracted for productive uses. Engine exhaust provides the highest temperatures and the greatest heat output.
The typical exhaust temperature is about 860°F. Exhaust heat can generate intermediate-pressure steam for purposes such as boiler feed water heating, and low-pressure steam for processes such as sterilization, pasteurization, space heating, tank heating, humidification, and others.
More possibilities are created by supplemental firing with natural gas, which can increase exhaust temperatures and heat output to produce steam at greater volumes and pressures. Heat can also be extracted from the engine jacket water to produce warm or hot water at temperatures of up to 210°F for space heating and a variety of industrial processes. Lower-quality heat—if not included in the jacket water circuit—is available from the oil cooler and the second stage of the after-cooler to meet additional low-quality hot water applications.
Steam or hot water can be passed through heat exchangers to create hot air to feed equipment such as kilns and dryers. The heated air is mixed with fresh outside air to enlarge the volume and enable precise temperature control.
Steam, hot water, or exhaust can be passed through absorption chillers to produce cold water for space or process cooling. Absorption chillers use heat instead of electricity as the energy source. Their efficiency is measured by coefficient of performance (COP). Simple, relatively low-cost single-effect absorption chillers are activated at temperatures as low as 200°F; COP typically ranges from 0.7 to 0.9. More complex double effect units activated at 347°F deliver higher COP of 1.05 to 1.4, although at greater upfront cost.
Heat-recovery systems can be configured to deploy some heat for water and steam production and the balance to absorption chillers in a trigeneration setup. Alternatively, systems can produce space heat in winter and air conditioning in summer.
Where a site requires continuous prime power and has little or no heat load, engine exhaust heat can be used to boost electrical output through the organic Rankine cycle. The exhaust, typically from multiple engines, feeds a boiler that converts a working fluid to vapor, which in turn passes through a turbine. This configuration, similar to combined-cycle electric power plants, can boost generating capacity by roughly 10% and improve electrical efficiency by five to six percentage points, says Devine.
Heat pump technology can extract useful heat from lower-quality heat sources such as the engine aftercooler circuit, residual heat from the exhaust downstream from the exhaust heat recovery boiler, and even radiant heat from the engine block. This heat can be used to preheat the engine jacket water heat recovery circuit or for low-temperature space or process heating. Such heat pump installations actually can raise overall system thermal efficiency to slightly greater than 100%—based on the fuel low-heating value—with the recovery of heat lost due to the latent heat of vaporization in the combustion process, the difference between the low and high heat value of a fuel.
Beyond heat recovery, carbon dioxide in the exhaust gas is a usable byproduct of power generation. Engine exhaust rich in CO2 can be cleaned in a catalyst reactor, cooled and fed to a process. “In greenhouses, for example, CO2 fertilization helps crops grow faster, improving yields by 10 to 20%,” says Devine. “Exhaust gas also can provide a low-cost source of CO2 for industrial applications or even for carbonation in soft drink bottling. Taking efficiency to the ultimate level, a single generator set can deliver electricity, space or process heating, space or process cooling, and CO2— a concept known as quadgeneration.”
Heat Recovery From Many Processes
Cogeneration is not limited to highly engineered systems that maximize production of both electricity and heat, Devine points out. “Simple and well-conceived heat recovery can improve the economics of many electric power projects with only a modest additional investment,” he says. “Almost any application that entails roughly 1,000 or more annual operating hours offers potential for economical heat recovery. The only firm requirement is that the value of heat recovered outweighs the added cost of the heat-recovery and control mechanisms.”
Heat recovery from the engine cooling circuit is simple, Devine says.
“A shell-and-tube or plate-and-frame heat exchanger can produce water at 180 to 210 degrees Fahrenheit, depending on the engine jacket water temperature,” he says. “This water can serve purposes that include space or domestic water heating, light production process heating, and boiler condensate or make up water preheating, as well as air conditioning, process cooling, and desiccant dehumidification.” In each case, the recaptured heat displaces some costs for fuel or utility electricity, Devine says.
“To the extent that the recovered heat supports energy needs during times of peak electric load, total demand, and, thus, demand charges are also reduced,” he says.
Examples of low-intensity, limited-duty cogeneration include as follows.
- Commercial real estate: Office buildings can cost-effectively operate generator sets during business hours, avoiding utilities’ highest time-of-use rates. If heat recovery from a jacket-water heat exchanger can partially offset the cost of fuel for space heating, water heating, or dehumidification, then return on investment improves.
- Light industry: A small- or mid-sized manufacturer with an onsite generator set could install a heat exchanger in the engine cooling system loop, with a thermostatically controlled diverter valve to regulate the flow to the in-plant load, thus cost-effectively satisfying a variable hot water requirement.
- Hospitality: Hotels can readily use heat recovery for domestic hot water, laundries, kitchens, or swimming pool heaters. In summer, the recovered heat can power absorption chillers or desiccant dehumidifiers for space conditioning.
- Food processing: Food producers can recover exhaust and jacket water heat to create low-pressure steam for light process loads such as cooking or raising dough, or to produce hot water for cleaning and sanitizing. Depending on the size and character of the heat load, such systems can be cost-effective in single- or multiple-shift service, even if heat demand is cyclical or seasonal.
|Photo: Energy Concepts
air chiller also
Cogeneration With Gas
Advances in gas engine technology have been essential to progress in cogeneration, says Devine. “By nature, gas engines serve well as isolated or grid-connected onsite power sources,” he adds. “They offer high power density, low first cost per kilowatt, and quick, simple installation. Fuel and operating costs are competitive, emissions are clean, and service is readily available with an abundance of trained and qualified technicians worldwide.”
The basic engine technology is highly reliable, Devine points out.
“Uptime can approach 98%, including all maintenance and repairs,” he says. “Engines readily handle full or part loads, tolerate varied altitudes and ambient conditions, and can be brought online quickly. The latest engines develop high power output in footprints up to 50% smaller than traditional units, fitting easily in small engine rooms or containerized power plants.”
Gas engines are well suited to operate in cogeneration service on refined natural gas and propane, as well as on fuels of variable heating value and purity, Devine says.
Landfill gas, agricultural biogas, and wastewater treatment plant digester gas may produce exhaust containing corrosive compounds, requiring stainless steel surfaces in exhaust gas heat exchangers, but no special modifications are required for heat recovery from liquid cooling circuits. Other specialty gases like coke gas and coalmine methane are also viable cogeneration fuels.
Advances in Engine Technology
The latest engines, proven in multiple applications all over the globe, use a variety of digital microprocessor-based monitoring and control technologies that include the following.
- Air/fuel ratio control based on charge air density, maintaining NOx (nitrogen oxide) emissions within the tightest available tolerance under all ambient and load conditions irrespective of changes in air temperature and humidity
- Air/fuel ratio control based upon Total Electronic Management systems that optimize generator set performance, measuring each cylinder’s temperature and adjusting combustion to minimize fuel consumption and engine emissions, and prevent detonation
- Control system strategies that can be configured to control functions beyond the engine itself, such as radiator motors, electrical breakers and systems, and even a complete cogeneration plant
- Detonation sensing by individual cylinder with automated control to retard timing if detonation occurs. These engines are designed with intake systems that enable efficient air flow and minimize heating of charge air, increasing the air/fuel charge to the cylinders for optimum performance. An open-chamber cylinder design and low-pressure fuel system [0.35–35 kPa (0.5 to 5 psi)] eliminate the need for a fuel compression skid, and the skid’s subsequent cost and ongoing operational expense.
Other advances in engine technology include as follows.
- Optimized air and exhaust flow: Both the inlet and the exhaust system are tuned to enable highly efficient, laminar flow. A technology called Pulsed Energy Advanced Recovery Line (PEARL) uses flow-optimized exhaust pipes that convey a constant exhaust mass flow to the turbochargers. Each PEARL module evacuates the exhaust of two cylinders. Exhaust flow is timed so as to keep the turbocharger spinning at the optimum speed over the engine’s entire operating load range. Precise ignition timing—automatically adjusted by cylinder for fuel quality changes—augments the entire process.
- Miller cycle: This adjustment in the combustion cycle by itself increases fuel efficiency by about one percentage point. The Miller cycle differs from the more traditional Otto cycle in that the intake valves close not when the piston reaches bottom dead center, but at typically 10 to 15 degrees before bottom dead center in the early inlet close version. As the piston continues down with the intake valves closed, the air/fuel mixture expands and cools, increasing the detonation margin. This enables a higher compression ratio of 14:1 or 15:1, versus 11:1 or 12:1 for the Otto cycle, and is designed for higher fuel efficiency.
- High-energy ignition: Pre-chamber spark plug technology, improved with optimized plug geometry. The spark plugs admit air and fuel through small orifices and upon ignition eject flame through the same orifices. High-energy ignition coupled with pre-chamber plug technology enables the engine to operate on a significantly lean fuel mixture without risking lean misfire, thus sustaining high power output and low emissions over extremely long life spans.
In recent years, an alternative approach to off-the-shelf engines has emerged in the form of individual generator sets customized to fit the application, Devine says. “Rather than purchase an engine and accessory package based on published ratings and a price list, users provide a sample of the fuel expected to be used, describe the ambient conditions and altitude, and specify the application and key operating objectives such as top fuel economy, lowest emissions, block loading capability,” he says, adding that the manufacturer then custom-designs a gas engine-generator system to fit those criteria.
In the range of customization options available, application engineers can select from a variety of compression ratios, pistons designed for specific fuel types, different turbochargers and nozzle ring configurations, and site-specific air system operating and engine timing maps.
“The customized units come with further advances in engine technology that expand the limits of engine control and reach new heights of efficiency—up to 44% electrical efficiency in the generator sets alone and up to 90% total plant efficiency in cogeneration or trigeneration service,” says Devine. The technology advances contribute to a new paradigm in maintenance intervals, he adds. “The intervals for spark plug replacement and oil changes are designed to be the same at 4,000 hours—some six months of continuous operation, or more than double the interval expected with traditional technology,” says Devine.
After about eight hours of planned downtime for service, the engine is ready to run for another six months, he adds. Cylinder head overhaul intervals are at approximately 32,000 hours and major overhaul intervals are approximately 64,000 hours with fuels containing contaminants or impurities, dictating shorter intervals. Operating costs are further reduced by lowering oil consumption: engine technology innovations have cut oil consumption by as much as half, a savings of 500 gallons and $10,000 per year on a 20-cylinder engine-generator rated at 2 MW, says Devine.
The Economic Question
Every cogeneration project comes down to a question of economics, Devine points out: “Will savings on energy costs and revenue from electricity generated provide adequate return on the investment in equipment?” In general, he says, the outlook is most favorable where:
- The utility electricity cost is relatively high.
- The fuel price is relatively low.
- The system will operate with a high electrical and heat load factor.
- Electric and thermal loads coincide during a typical day.
- The site requires high reliability and power quality.
- The cogeneration system can double as a standby power source.
The availability of a low-cost “opportunity fuel” such as anaerobic digester or landfill gas generally improves the economics, Devine says. In particular, digester gas-fueled cogeneration is a key contributor in a growing quest for energy self-sufficient wastewater treatment plants.
In exploring project design alternatives, engine fuel efficiency is one of many considerations. “For example, capacity factor—the percent of total theoretical output the generators actually achieve—may far outweigh fuel savings,” he says. “Furthermore, if high efficiency comes at the cost of increased downtime from more frequent maintenance or engine sensitivity to fuel variability or quality, or if performance is degraded at higher ambient temperatures, then project economics are compromised.”
Other engine capabilities such as low emissions or fast response to block loads may also be more important than fuel economy in some settings, he adds.
For the development of most CHP projects, it takes specialized expertise to determine how best to deploy the equipment on a site and to evaluate the project economics. Devine advises that it’s best to check for fatal flaws—such as physical or cost barriers that would make the project impractical—before investing in a full feasibility study. For example:
- Will it be impossible or extremely expensive to acquire an air-quality permit?
- Will it be difficult to secure a wastewater permit to discharge cooling water or exhaust condensate?
- Is the available space on the site too small to accommodate the engine and heat recovery equipment?
- Will the natural gas service need a costly upgrade to deliver the necessary fuel?
- Is the facility’s electric power infrastructure inadequate to distribute the generated power?
- If the project success calls for excess electric energy generated to be exported to the grid, do local utility policies preclude such sales?
- If exporting power to the local utility is possible, is the power purchase price too low to allow for profitable operation?
“If the answer to one or more of these questions is ‘yes’, then you will want to consider the impact of resolving the issue on the project economics and the impact that the resolution will have on project feasibility,” says Devine.
If nothing stands in the way at that point, the next step is a high-level look at project economics, Devine says. “This involves estimating and stacking the component costs and savings—or revenues—per kilowatt-hour to arrive at the net benefit,” he says, adding that a local power-generating equipment dealer can be a good source of reasonable, experience-based estimates. The major cost components are:
- fuel, typically the largest item at 60 to 80% of project operating cost, unless an opportunity fuel is available
- capital recovery: principal and interest on the equipment investment
- operations and maintenance—staffing, components and supplies for daily operations, periodic service and repairs
From the total of these costs, the thermal credit—the economic value of the recoverable heat—is deducted. “This is typically done by looking at the cost per kilowatt-hour of replacing the existing thermal system with a higher-efficiency system,” he says. “If the resulting total net cost per kilowatt-hour is significantly lower than the retail price of electricity, including demand charges, then the project probably merits further investigation through an engineering study.”
In the analysis, it is essential to understand utility electricity costs in detail, including on- and off-peak energy prices, on- and off-peak demand charges, standby charges, and any non-availability penalties and existing or pending cogeneration incentives from the local utility or government entities, Devine points out. Ideally, a project should be developed in a cooperative relationship with the local utility, he says.
“For example, a project that reduces the user’s overall energy costs while helping the utility limit peak demands on its grid provides a win-win and may even benefit from utility incentives that enhance economic payback,” says Devine.
Another benefit of a cogeneration system is that it can function as a standby power source, although not for life-safety electric loads such as hospital operating suites where diesel standby with onsite fuel storage is required, Devine points out. “In today’s emission-conscious environment, demand is growing rapidly for gas-fueled standby generators,” he says. “Such systems, installed for utility-parallel cogeneration and operated for extended hours continuously provide electric power security while also generating revenue.”
Devine says few organizations have the in-house expertise to plan and implement cogeneration projects. Equipment suppliers and consultants can provide vital support from project planning through design, financing, construction, operation, and maintenance. “An appropriate project partner should have a deep understanding of cogeneration and a track record for completing profitable projects,” he points out.
CHP Modules—Standard and Custom Built
Elite Energy Systems provides pre-engineered “standard” CHP modules, as well as custom-built solutions for commercial and industrial energy users; these are powered by Caterpillar engines with multiple fuel options including natural gas, biogas and LPG (liquefied petroleum gas). The most common project sizes are in the 150-kWe to 2,000-kWe size range, with multiple units extending beyond that range.
Elite’s systems incorporate synchronous or inductive generators, seismic isolation, sound attenuation, ultra-low emissions, sound-eliminating air ducts, integrated design, stainless exhaust, rain-tight construction, removable door and roof sections for maximum serviceability, on-board primary containment, separated controls cabinet, battery charger, stored energy breaker, and Internet connection for remote system monitoring.
Elite designs CHP systems that focus on the optimum use of the recovered waste heat created while generating electricity. The recovered heat comes from the engine coolant circuit and exhaust gases, and is effectively “free energy.”
The most common applications focus on providing heat for process heating such as domestic hot water and swimming pools. The use of the recovered waste heat is an alternative to burning fuel in a boiler or using electricity for heating. CHP systems also can be designed to generate chilled water using an absorption chiller that uses the recovered waste heat as its energy source. In addition, CHP systems can be designed to generate low-pressure steam.
For agriculture, Elite also designs, manufactures, and owns anaerobic digester systems that operate on this formula: six digesters plus two CHP modules which produce 300 kW of electricity as well as organic soil amendment and compost tea. These modular systems are sized for about 1,500 lactating cows. Elite operates its own manufacturing and testing facilities to ensure its systems meet or exceed the demands of the customer site requirements while meeting stringent air emissions regulations.
The company has designed systems to operate in both parallel and island modes and maintains interconnection agreements with many publicly held and private utilities, including net metering installations for power sell back to the grid. The operation of Elite’s CHP systems are remotely monitored, interrogated, and controlled using control system technology designed with an interactive interface to enable the user to communicate with the CHP system 24/7.
One project in which Elite has been involved is the John Muir Medical Center, a 259-bed acute care facility in Concord, CA. In summer 2010, the company was commissioned to design a system to help the medical facility incorporate green building technologies that would include energy efficiencies in its expansion project.
The system consists of three 250-kWe CHP modules and one 150-kWe CHP module for a total of 900 kWe powered by three Caterpillar 3412 engines and one Caterpillar 3406 engines, all running on natural gas. Heat from the engine exhaust is captured with jacket water to provide hot water to the hospital, and an absorption chiller also provides seasonal cooling to the facility.
The system was created to provide a number of benefits to the medical center including more than 86% total fuel efficiency in contrast to 27% for the utility, displacement of electricity from the utility for similar costs with distributed generation, the creation of additional thermal energy at no cost, the reduction of power demand charges from the utility, the enhancement of power quality and reliability, an eligibility for energy efficiency grant programs, redundancy for electrical and thermal energy, and lowering greenhouse gas emissions and carbon footprint.
Don Erickson, president of Energy Concepts Company, points out that much of the global energy demand is thermal—either for heating or cooling. “Too often, those thermal demands are met wastefully,” he says. “For example, by using prime fuel to produce low grade heat, by rejecting waste heat, or by supplying thermal needs from electricity.”
Energy Concepts is commercializing heat-activated cycles powered by otherwise wasted availability instead of prime fuel. Applications range from hot water heat pumping, chilling, industrial refrigeration, LNG (liquefied natural gas) production, light ends recovery (flare gas elimination), ice production, desalination, and others, including power production from waste heat.
“Waste heat has been termed the world’s greatest under-exploited energy resource, and Energy Concepts technology derives greater value from waste heat,” points out Erickson. “Our technology is a key enabler for more economic CHP systems. We offer large-scale savings at two- to three-year paybacks.”
Energy Concepts designs, develops, and manufactures energy-efficient, heat-activated absorption systems and fluid contact equipment. The ammonia absorption systems produce refrigeration, heat pumping, space conditioning, and/or power. There is a wide range in system capacity, from small residential to large industrial equipment powered by waste heat, solar heat, or prime heat.
Those systems that upgrade waste heat to achieve greater value than simple heat recovery include the ThermoSorber thermal heat pump, ThermoCharger turbine inlet air chiller (also known as ARCTIC), engine interchiller, ThermoChiller waste heat powered refrigeration/air-conditioning system, and HeliChiller solar thermal refrigeration/air-conditioning system. A chilling economizer for steam boilers, heat recovery steam trap, condensate tank heat recovery, steam heat pump, ISAAC solar icemaker, plus new heat exchanger geometries and new distillation and desorption column configurations also advance the potential of waste heat for numerous processes. Dual function absorption cycle power and refrigeration from waste heat, absorption power cycle, steam-ammonia power cycle, and liquid desiccant chiller are all being developed by Energy Concepts.
In April 2011, Energy Concepts Company rolled out its new “standard design” Thermal Heat Pump (THP). The initial production model was designed with a heating capacity of 175-kW (600,000 BTU/hour) and 70-kW chilling capacity (20 tons) to be powered by 105 kW (360,000 BTU/hour) input heat and 2 kW electricity.
Thermal Heat Pumps are powered almost entirely by heat rather than by electricity, a technology that conserves gas and electricity. It does not exacerbate peak electric demand in summer and winter and is designed to reduce demand peaks. Waste heat, exhaust, or solar thermal heat can power the THP, which offers a return on investment (ROI) averaging two to three years.
The Helisorber is a recent addition to the company’s line-up and serves as a solar chiller/thermal heat pump. It is designed to double the useful output from a solar thermal collector. For example, supplying 100 kW of thermal heat from a collector to the Helisorber will yield 75 kW of 44.6°F chilling, plus 175 kW of hot water heating to 140°F.
The California Energy Innovation Small Grant Program funded development of its prototype. That unit produces 87 kW (25 tons) of chilling and 215 kW of water heating from 130 kW thermal fluid heat input. The design has been optimized and scaled to refrigeration capacities from 10 to 200 tons (35 to 700 kW). In order to operate at this level, the chilling and heat pumping are produced simultaneously, so both must be used, stored, or lost. Additionally, the driving temperature must be 257°F or higher.
The technologies are used in several sections of a plant or mechanical system, including steam generation, steam distribution, refrigeration system (generation and use), hot water heating system (generation and use), distillation, and desorption. The technologies also are designed to make more efficient the industrial plant that generates its own power, including making more beneficial use of the reject heat.
Among the many applications of the technology is a 2,000-ton ThermoCharger (ARCTIC) system commissioned in central Texas in 2010 that chills turbine inlet air on a LM6000. It delivers 2,000 tons of exhaust heat-powered chilling with less than 200 kW of parasitic load.
The system eliminates the need for tempering air fans, medium voltage step down transformers, and an anti-icing system. The ARCTIC system delivers constant 48°F inlet air under most ambient conditions to boost the LM6000 output by 11 MW on the hottest days of the year.
At a 2009 installation financed by Clean Tech Partners and installed by Bassett Mechanical at a meat packing plant in Green Bay, WI, is a 300-ton ThermoSorber (TS-300) that produces 10.5 million BTU per hour of 135°F hot water plus 300 tons (1,000 kW) of 34°F chilling from 7,500 pounds per hour of 100 psig steam.
A thermally activated refrigeration plant was recently developed and deployed to a Kansas natural gas field. The air-cooled ammonia absorption refrigeration plant, ThermoChiller, chills one million standard cubic feet per day of wellhead gas to -20°F. The chilling condenses out 1,200 gallons per day of natural gas liquids (NGL), necessary to upgrade the gas to pipeline specifications and provide propane and butane NGL byproducts. The ThermoChiller is powered by the ethane gas rejected from both the pipeline gas and the NGL, which otherwise would be flared. The ethane heats a glycol heater supplying 380°F glycol to the ThermoChiller.
The skid-mounted ThermoChiller is designed to operate at 110°F ambient temperature. It requires 5 kW of electric power for the cooling fan and three small pumps. All electrical and instrument leads are via plug-in cables. The data acquisition system is equipped for remote monitoring.
The ThermoChiller is available in capacities from 10 tons to 200 tons of refrigeration. It also can be applied to cold storage warehouses, blast freezers, siloxane removal at landfill gas recovery plants, and anaerobic digesters for wastewater treatment plants.
At the Auction Block Company, a seafood processing company in Homer, AK, the ThermoChiller is playing a role in a refrigeration system onsite. A blast freezer serves the fish freezing needs of the Cook Inlet commercial fishing fleet. While electricity and oil are expensive in Homer, coal is readily available and inexpensive. Coal is burned in a boiler to produce 320°F hot water in a ThermoChiller ammonia absorption refrigeration plant.
Thirty-six tons of refrigeration is produced at -40°F. The refrigeration is transferred to CO2 at 35°F and is pumped to the blast freezer. The blast freezer coils are defrosted with hot glycol. The 36-ton ThermoChiller is cooled by an air cooler in the colder months and by 46°F seawater in the summer. When there is no demand for blast freezing, the ThermoChiller refrigeration is diverted to a flake icemaker system to produce 18 tons of flake ice per day.
The Saskatoon Boilers have indicated an “exceptionally clean” exhaust gas with virtually no soot or VOCs.
The overall system integration of the CO2 blast freezer, icemakers, ice storage, coal boilers, and ammonia absorption refrigeration was supervised by Walt Kallenberg of Anchorage, with assistance from Energy Sea and Central Peninsula Refrigeration. Where coal is expensive or not readily available, the boiler can be fired with wood chips, making this a candidate for the world’s first renewable energy–powered blast freezer, according to Energy Concepts Company.
This absorption refrigeration product is available in capacities from 10 to 100 tons. It is engineered to order for whatever heat source is available, be it exhaust gas, solid fuel, natural gas, solar thermal, or geothermal.
Where water is scarce, an air-cooled version is available.
Less Stress on the Grid, Fewer Greenhouse Gases
Dresser-Rand has a line of gas-fired CHP packaged systems ranging from 180 kWe to 1.3 MWe per unit.
“These Guascor engine-based systems are easily made into trigeneration units with the simple addition of a factory-assembled absorption chiller section, turning the CHP into a CCHP,” notes Steve Zilonis, director of business development.
“The units can run prime power and add increased resiliency to a site for unplanned outages as well as they have the ability to burn all kinds of renewable fuels such as biogas and wood gases and landfill gas, among others,” he says. In the biogas CHP sector, the company has more than 250 units installed in the US for renewable energy “cow power” dairy farm CHP projects.
“The CHP systems come in both rich and lean burn engine platforms, which means we can easily fit after treatment for emissions systems to run in all US states and worldwide and reduce greenhouse gases,” says Zilonis.
While an ROI is site-dependent, “in the US, there are many states offering very large incentives for CHP, and both the Obama administration and the American Gas Association have confirmed there is still more than 40 gigawatts electrical of potential CHP to be done in the country,” points out Zilonis.
Properly applied, CHP may save up to 50% of a site’s energy bills in an average installation, Zilonis says, adding that a site such as a college campus or hospital can derive “tens of thousands, to millions of dollars a year in energy savings,” depending on the sites’ current energy bills.
“It also has societal benefits of adding grid support and stability,” he adds. “It creates jobs, helps reduce greenhouse gases, and is the largest single available technology to increase conventional efficiencies in electric and natural gas use.”
Zilonis says that “the world built an electric grid based on wires and central power generation. As generators typically only convert 30% of their fuel to electricity and the other 70% is released as waste heat, we only get 30% of the fuel we consume in power plants in the form of electricity.
“By putting the CHP plant in the building onsite, we still make power at 30% efficiency, but now we get to use the waste heat from the generator instead of buying natural gas or oil for heating or cooling,” he continues. “Now we use our energy at 70 to 80% instead of only 30%, so that’s a large increase in efficiency.”
By using heat with CHP, fuel usage—a large contributor to greenhouse gas—is saved, Zilonis says. “Anytime you burn fuel, you produce greenhouse gases. CHP is the most effective use of dollars to reduce greenhouse gas emissions as compared to both wind and solar for their energy benefits, although in 2013 solar started catching up quickly, seeing a 70% reduction in PV costs since 2011.”
Addressing how the system takes the strain off of the grid, Zilonis points out how “the grid has to transport lots of electrons around for all the customers of the electric utility. As more customers and buildings go in, the more stress this puts on the grid to deliver these new sites reliable power. Nothing relieves the stress more from the grid than decentralized energy, power produced at the point of use.” A site such as a college or hospital that makes 1 MWe of CHP power is keeping that 1 MW out of the wires that travel across the state to the site, adding grid strain, he adds.
“After Superstorm Sandy, the Department of Energy and newly appointed Secretary Ernest Moniz visited New Jersey and discussed the benefits of smaller microgrids being built inside the main network electric grids and being powered with CHP and decentralized power sources to help add resiliency and take strain off the main power grid for increased reliability and stability in natural disaster situations,” points out Zilonis.
One of Dresser-Rand’s most notable installations is at Boston Scientific in Marlborough, MA. The site utilizes a Dresser-Rand 555-kWe-130 Ton Trigeneration Unit with Solar Thermal Assist roof systems, and it paid for itself within the first three years of operation.
“It was the first CHP system to enter into the newly developed Green Communities Act program in Massachusetts,” says Zilonis. “This entailed being part of the first US greenhouse gas cap and trade group with the Regional Greenhouse Gas Initiative, of which 10 New England States are part of the carbon trading program.” The Boston Scientific site currently trades CO2 offsets for ~$20 per MWh, about $75, 000 per year and saves more than $4 million per year in energy costs for the site.
The project received the Association of Energy Engineers Award for 2010 Best CHP Project in New England.
The Work of Turbines
MAN Diesel & Turbo tailors its systems, offering engines and turbines out of one hand to achieve the highest efficiencies in the market, says Simon Lott, head of power solutions. “We use state-of-the-art technical design—like reaction-type blading on turbines—to ensure the highest engine/turbine efficiency.”
That comes with a higher capital cost investment, he adds. “However, depending on the application and energy costs, we see simple returns on the extra investment (cost above market price) between two to five years, having a significant impact on the projects’ long-term net present value.”
Case in point: a newly developed gas turbine from MAN Diesel & Turbo can generate an output of 6 MW of electricity. Its approximate 4-meter high size enables the unit to be used wherever electrical energy is needed, including remote locations such as an oil platform or a mini power plant for residential areas. An electronically
controlled and computer-monitored communication unit links the entire package with the customer’s control room. An input air filter ensures only filtered air enters the gas turbine. The oil cooler keeps the gas turbine system’s lubricating oil at the right temperature.
Power heat cogeneration is designed to utilize fuel twice as effectively, producing both electricity and heat, which would otherwise escape through the chimney, allowing for 80% utilization of the applied energy.
In the heat exchanger, the exhaust heat from the turbine turns water into hot steam that can be used for other applications, such as drying or melting a variety of products. The gas turbine drives a generator and supplies electricity.
A gas turbine engine unit operates by hot gas generated in the combustion chambers, causing the turbine blades to turn, converting thermal energy to mechanical energy, which initially drives the compressor. In the single-shaft design, all of the compressor and turbine systems are lined up on the same shaft.
The twin-shaft machine serves as a mechanical drive, such as for compressors in the oil and gas industry. In the twin shaft design, the compressor and the gas generator turbine form a single unit. The same housing contains the power turbine, which also is used as a mechanical drive in gas or oil pipelines, or serves to produce power through a generator.
Ambient air is first sucked into the system through the inlet housing. The adjoining compressor is equipped with 11 rows of blades of varying sizes. The largest blade is the size of a slice of toast; the smallest is the size of a dime. Step by step, the air is increasingly compressed and driven into the combustion chambers at high pressure.
The air blends with a gaseous or liquid fuel, ignites, and combusts. One part of the air intake is diverted from the combustion chambers and serves to cool the surrounding environment, which can reach a temperature of up to 1,200°C (2,192°F).
The smaller drive supplements more powerful THM turbines from MAN Diesel & Turbo with outputs exceeding 10 MW. The system is designed to be long-lasting, robust, easy to maintain, low in emissions, versatile, and offering a high degree of efficiency when working at less than full capacity.
The gas turbine assumes a role in the field of regenerative energy when solar and wind power do not always deliver power consistently, company marketing materials point out. According to MAN Diesel & Turbo, the gas turbine systems are in increasing demand in power stations that work according to the power heat cogeneration principle, resulting in a more efficient use of energy than when heat and power are produced separately.
Combined gas turbine and steam turbine systems direct exhaust gases from the turbine to a waste heat boiler that produces steam. This drives a downstream steam turbine that yields additional electricity. The steam’s residual energy content at the turbine outlet can be condensed in a cooling tower or used to generate more heat. In comparison with pure gas turbine operations, this results in a significantly higher degree of efficiency, with a gain of more than 30% in electricity production. In coupled operations, a fuel utilization level of around 80% is achievable. The system has a projected life cycle of 30 years or more, influenced by fuel costs and maintenance.
With other fuels such as synthetic gases, biodiesel, and bioalcohol growing in importance, the design of the new gas turbine with its six small combustion chambers is designed to make it easily adaptable for a variety of fuels.
In terms of maintenance, a complete turbine replacement can be carried out within 72 hours. MAN Diesel and Turbo’s maintenance system involves online monitoring that detects abnormalities and immediately introduces appropriate measures as well as a borescope, which allows for the examining of the interior workings of the turbine without any disassembly.
Taking Cues From the European Market
2G CENERGY offers “all-in-one” modular CHP systems complete with integrated controls and switchgear, designed for fast integration and 100% plug-and-play. The company also offers complete biogas treatment systems, around-the-clock technical assistance, and support. 2G’s products range from 80 kW to 3 MW for natural gas cogeneration units.
“Our sweet spot on the natural gas side is between 150 kilowatts and 2 megawatts, and most customers utilizing cheap natural gas fuel typically purchase units between 250 kilowatts and 1.5 megawatts,” says Michael Turwitt, president and CEO of 2G CENERGY.
The reciprocating engines used by 2G are sourced from European manufacturers MAN, MWM (owned by Caterpillar), and GE Jenbacher (a division of GE Energy), and were designed from the crankcase up to combust gas, Turwitt points out.
In its system, 2G has leveraged its background in the CHP-heavy European market, as opposed to the US market where most gas-fired generators are sold for power only, says Turwitt. In the European market, thousands of CHP units have been in operation for many years, he adds.
“CHP: everyone knows what CHP is in Europe,” he says. “In the US, people often say, ‘I need a genset,’ when they mean CHP. Then they learn that the engine-generators offered by engine dealers are only a small portion of the entire package and are by no means a complete cogeneration system.
“The company has integrated the entire heat extraction technology and other components, such as absorption chillers for customers who need cooling, into a family of modular plug-and-play products that range from 80 kilowatts electrical to 3 megawatts electrical,” he says. “They are virtually ready to connect to the host building electrical and heating systems, as well as the regional electricity grid.”
2G products can be hooked up by a contractor or a 2G CENERGY employee with the electrical connection at the breaker, the gas connection, and the thermal energy supply and return. In most cases, the products are shipped as fully containerized modules and installed outside the building for cost effectiveness.
“The fully engineered and manufactured CHP cogeneration product is especially attractive to customers who seek reliability, perfect functionality, and the most cost-effective value for money solution,” says Turwitt. End users are typically those seeking simultaneous electricity and heat production, as well as cooling and/or other thermal energy applications, he adds.
“The economic benefits include much cheaper electricity and energy costs, dramatically increasing energy efficiency, preventing loss by avoiding power outages, exceeding environmental standards—it increases the users’ public standing and image as a clean and green company—and avoids fines,” says Turwitt. “In addition, many public incentives are available, depending on location and state.”
A typical ROI ranges from two to five years, depending on the individual application and specific circumstances, he adds.
While states offer different incentive programs such as grants, loans, utility, and tax incentives, 2G CENERGY also offers finance and leasing solutions.
One of the company’s CHP systems, the patruus 380, has been installed at Calgary International Airport in Canada. The installation is part of an airport expansion and features four 2G natural gas-fired CHP cogeneration modules, each producing up to 355 kWh of continuous electricity and up to 475 kW, each of thermal energy which will be delivered to the building in the form of hot water at more than 88% efficiency.
The modules are complete solutions including sophisticated CHP controls, heat recovery technology, advanced gas train, sound enclosure with space ventilation, and special silencers. They will serve the needs of an expansion that incorporates sustainable design principles into a new international concourse that will create more space, while reducing energy consumption and minimizing environmental impact. The new terminal is scheduled to open in October 2015 with five levels and 22 new aircraft gates, a new hotel connecting the new and existing terminals, a new runway, and a new control tower.
Rolls-Royce offers gas turbine generating sets for the distributed energy environment from 4 MWe to 64 MWe designed with dry low-emissions combustion systems, and reciprocating gas engine generating sets ranging from 2 MWe to 9.3 MWe. The company’s focus market is power generation and oil and gas customers, says Jonathan Li, plant executive for Rolls-Royce Energy Systems.
“Our offering from a cogeneration standpoint is focused around our gas turbines which are aeroderivative gas turbines,” says Li. “All of our gas turbines were originally designed for use on airplanes, and we take that same technology and its key attributes and convert it to generate power and electricity. Our aeroderivative gas turbines range from three to five megawatts in our 501 product range, then around 25 to 40 megawatts, which is our RB211, and then from 50 to 64 megawatts, which is the Trent 60.”
The Rolls-Royce Trent 60 aeroderivative gas turbine is designed to deliver up to 64 MW of electric power in simple cycle service at 42% efficiency. The industrial RB211 is derived from the aerospace RB211, the chosen powerplant for several large airliners. Auxiliary equipment for intake air filtration, acoustics and lubrication are part of the Rolls-Royce scope of supply for oil and gas and power generation applications.
The RB211 gas turbine package is designed to match the Rolls-Royce gas generator with the efficiency of the RT62 or RT61 power turbine. The gas turbine systems have been installed in remote and offshore applications. Dual fuel Dry Low Emissions (DLE) and non-DLE models are available for both mechanical drive and power generation applications.
“Globally and domestically, there is a drive toward a lower carbon footprint to lower emissions and have greener technology,” points out Li. “From a fossil fuel standpoint, the one that offers the lowest carbon footprint and emissions comes from natural gas, and natural gas turbines as well, because of the low NOx technology, the low-emissions technology that is available with gas turbines.”
In addition to offering a low carbon footprint, Rolls Royce also offers operational flexibility, Li says. “The equipment can be started and stopped very quickly. It can operate at different loads to have good efficiency. Renewable power—wind power, for example—is sometimes not very secure.”
Where there is a desire for cogeneration without the need for a large system there are products such as Marathon Engine Systems’ ecopower micro cogeneration systems (microCHPs), which provide heat and electrical power utilizing advanced cogeneration technology designed for high overall efficiency, lower emissions, and quiet operation.
The ecopower micro CHP unit uses a natural gas or propane Marathon engine and power conversion technology to supply thermal and electrical power to the building and grid; in some cases, the facility can generate credit from a utility company, while simultaneously the heat from the engine is captured to create thermal energy and used to warm the building and/or create domestic or process hot water.
Mike Monohan, marketing and sales director for Marathon Engine Systems, says, “We are more than 90% efficient across the board on the unit, and we’re concentrating on residential and light- to medium-commercial type systems.”
The system is designed to emit significantly less carbon dioxide than a traditional powerplant—one ecopower will reduce the emission of carbon dioxide in the atmosphere by 33 tons a year. Waste heat is recovered through the system and recycled.
A typical installation consists of an ecopower microCHP system, buffer tank, boiler, and hot water tank. The ecopower advanced software in the system is engineered to enable the system to function more efficiently for energy demands by intelligently monitoring building conditions and adjusting the heat and electrical output to meet energy requirements. There also is an option to monitor the system via the Internet.
The software integrates the ecopower with the buffer tank, adjusting the system output to match the buildings thermal and electrical needs. An indirect hot water tank can be hooked up to satisfy water heating needs, enabling year-round electricity generation.
The ecopower system can be installed in parallel configurations with up to four units operating simultaneously. The system is designed for 4,000 hours between service intervals. The ecopower microCHP operates on a single-phase voltage of 240 VAC and at a frequency of 60 Hz. It measures 54 inches by 30 inches by 43 inches. The system has a power factor of 0.98–1, and an exhaust gas temperature of less than 180°F. Its electrical output range is 2.0 to 4.7 kW; its thermal output range is 13,000 to 39,000 BTU per hour; its gas consumption range is 0.21–0.65 therms per hour for natural gas, and 0.26–0.78 gallons per hour for LPG.
The system has an overall efficiency of 93%, with a power generating efficiency of 25%, a heat recovery of 68%, and waste heat of 7%. It has an average sound level of 1m 55 dB(A), and average NOx emissions of 0.005 pounds per megawatt-hour. The system won the 2011–12 ENERGY STAR Emerging Technology Award.
Monohan says his company is observing situations in which gas utilities are offering a CHP rate. “There’s a discount of anywhere from 20 to 35 cents per therm off if you’re using this type of technology, which is helping the ROI on the system,” he says. “Those are a lot of the things we’re trying to go after right now as far as where the markets are best for that.”
Additionally, in contrast to centralized power plants that throw all of thermal energy into the atmosphere, “we’re capturing all of the thermal energy and utilizing all of that first and using the electricity as a byproduct,” points out Monohan. “We feel the decentralized power approach is saving a tremendous amount as far as CO and NOx reduction and the energy savings.”
: Frequent contributing author Carol Brzozowski
specializes in topics related to technology and industry.
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