What is a Heat Recovery Steam Generator?

A Heat Recovery Steam Generator, or "HRSG" is a boiler that captures or recovers the exhaust of a prime mover such as a combustion turbine, natural gas or diesel engine to create steam.

Stated another way, a HRSG is used to recover energy from the hot exhaust gases in power generation. It is a bank of tubes that is mounted in the exhaust stack. Exhaust gases as much as 800 °F to 1200 °F heat these tubes. Water is pumped and circulated through the tubes and can be held under high pressure to temperatures of 370°F or higher which can be boiled to produce steam. Furthermore, the HRSG separates the caustic compounds in the flue gases from the occupants and equipment that use the waste heat. HRSG's are found in may combined cycle power plants.

"Once through" Heat Recovery Steam Generators operating with waste heat recovery from gas turbines (with supplementary firing and diverters in case the gas turbines aren't running at design load to maintain steam production) are also used in the oil and gas industry for Enhanced Oil Recovery applications, specifically for steam injection. Steam injection increases an oil  reservoir's pressure and reduces the viscosity of a "mature oil field." This type of Enhanced Oil Recovery iapplication is particularly beneficial for "heavy oil recovery." In fact, Steam injection is the optimum EOR application for reservoirs with low reservoir pressure field with heavy oil. Once-through HRSG's use the exhaust gas from nearby gas turbines and may use supplementary firing for producing additional steam.  Once-through HRSG's using the waste heat from gas turbines reduces the overall cost for steam injection.

CHP Systems (Cogeneration and Trigeneration) Plants 
Have Very  High Efficiencies, Low Fuel Costs & Low Emissions

The CHP System below is Rated at 900 kW and Features:
(2) Natural Gas Engines @ 450 kW each on one Skid with Optional 
Selective Catalytic Reduction system that removes Nitrogen Oxides to "non-detect."

The Effective Heat Rate of the CHP System below is 
4100 btu/kW with a Net System Efficiency of 92%.

Our CHP Systems may be the best solution for your company's economic and environmental sustainability as we "upgrade" natural gas to clean power with our clean power generation solutions. 

Our Emissions Abatement solutions reduce Nitrogen Oxides to "non-detect" which means our CHP Systems can be installed and operated in most EPA non-attainment regions!


What is "Cogeneration"?

Did you know that 10% of our nation's electricity now comes from "cogeneration" plants?

And because cogeneration is so efficient, it saves its customers up to 40% on their energy expenses, and provides even greater savings to our environment through significant reductions in fuel usage and much lower greenhouse gas emissions.

Cogeneration - also known as “combined heat and power” (CHP), cogen, district energy, total energy, and combined cycle, is the simultaneous production of heat (usually in the form of hot water and/or steam) and power, utilizing one primary fuel such as natural gas, or a renewable fuel, such as Biomethane, B100 Biodiesel, or Synthesis Gas.

Cogeneration technology is not the latest industry buzz-word being touted as the solution to our nation's energy woes. Cogeneration is a proven technology that has been around for over 120 years!

Our nation's first commercial power plant was a cogeneration plant that was designed and built by Thomas Edison in 1882 in New York. Our nation's first commercial power plant was called the "Pearl Street Station."

What is a Heat Recovery Steam Generator?

A Heat Recovery Steam Generator, or "HRSG" is a boiler that captures or recovers the exhaust of a prime mover such as a combustion turbine, natural gas or diesel engine to create steam.

Stated another way, a HRSG is used to recover energy from the hot exhaust gases in power generation. It is a bank of tubes that is mounted in the exhaust stack. Exhaust gases as much as 800 °F to 1200 °F heat these tubes. Water is pumped and circulated through the tubes and can be held under high pressure to temperatures of 370°F or higher which can be boiled to produce steam.

Furthermore, the HRSG separates the caustic compounds in the flue gases from the occupants and equipment that use the waste heat. HRSG's are found in may combined cycle power plants.

What is "Trigeneration"?

Trigeneration is the simultaneous production of three forms of energy - typically, Cooling, Heating and Power - from only one fuel input. Put another way, our trigeneration power plants produce three different types of energy for the price of one.

Trigeneration energy systems can reach overall system efficiencies of 86% to 93%.  Typical "central" power plants, that do not need the heat generated from the combustion and power generation process, are only about 33% efficient.

Trigeneration Diagram & Description
Trigeneration Power Plants' Have the Highest System Efficiencies and are 
About 300 % More Efficient than Typical Central Power Plants

Trigeneration plants are installed at locations that can benefit from all three forms of energy.  These types of installations that install trigeneration energy systems are called "onsite power generation" also referred to as "decentralized energy."   

One of our company's principal's first experience with the design and development of a trigeneration power plant was the trigeneration power plant installation at Rice University in 1987 where our trigeneration development team started out by conducting a "cogeneration" feasibility study.  The EPC contractor that Rice University selected installed the trigeneration power which included a 4.0 MW Ruston gas turbine power plant, along with waste heat recovery boilers and Absorption Chillers.  A "waste heat recovery boiler" captures the heat from the exhaust of the gas turbine.  From there, the recovered energy was converted to chilled water - originally from (3) Hitachi Absorption Chillers - 2 were rated at 1,000 tons each, and the third Hitachi Absorption Chiller was rated at 1,500 tons. The Hitachi Absorption Chillers were replaced shortly after their installation by the EPC company.  The first trigeneration plant at Rice University was so successful, they added a second 5.0 MW trigeneration plant so today, Rice University is now generating about 9.0 MW of electricity, and also producing the cooling and heating the university needs from the trigeneration plant and circulating the trigeneration energy around its campus.

Trigeneration Chart
Trigeneration's "Super-Efficiency" compared 
with other competing technologies
As you can see, there is No Competition for Trigeneration!

Trigeneration power plants are the ideal onsite power and energy solution for customers that include:  Data Centers, Hospitals, Universities, Airports, Central Plants, Colleges & Universities, Dairies, Server Farms, District Heating & Cooling Plants, Food Processing Plants, Golf/Country Clubs, Government Buildings, Grocery Stores, Hotels, Manufacturing Plants, Nursing Homes, Office Buildings / Campuses, Radio Stations, Refrigerated Warehouses, Resorts, Restaurants, Schools, Server Farms, Shopping Centers, Supermarkets, Television Stations, Theatres and Military Bases.

At about 86% to 93% net system efficiency, our trigeneration power plants are about 300% more efficient at providing energy than your current electric utility. That's because the typical electric utility's power plants are only about 33% efficient - they waste 2/3 of the fuel in generating electricity in the enormous amount of waste heat energy that they exhaust through their smokestacks.

Trigeneration is defined as the simultaneous production of three energies: Cooling, Heating and Power.  Our trigeneration  energy systems use the same amount of fuel in producing three energies that would normally only produce just one type of energy. This means our customers that have our trigeneration power plants have significantly lower energy expenses, and a lower carbon footprint.

What is a Waste Heat Boiler?

Waste heat boilers are a special type of boiler that generates steam by removing the heat from a process that would have otherwise been wasted. 

What is Waste Heat Recovery?

There are more than 500,000 smokestacks in the U.S. that are "wasting" heat, an untapped resource that can be converted to energy with Waste Heat Recovery technologies.

About 10% of these 500,000 smokestacks represent about 75% of the available wasted heat which has a stack gas exit temperature above 500 degrees F. which could generate approximately 50,000 megawatts of electricity annually and an annual market of over $75 billion in gross revenues before tax incentives and greenhouse gas emissions credits.

Waste Heat Recovery technologies represent the least cost solution which provides the greatest return on investment, than any other possible green energy technology or "carbon free energy" opportunity! 

Typical Waste Heat Recovery Installation

In some cogeneration and trigeneration designs, the exhaust gases can be used to activate a thermal wheel or a desiccant dehumidifier. Thermal wheels use the exhaust gas to heat a wheel with a medium that absorbs the heat and then transfers the heat when the wheel is rotated into the incoming airflow.

A professional engineer should be involved in designing and sizing of the Waste Heat Recovery section. For a proper and economical operation, the design of the heat recovery section involves consideration of many related factors, such as the thermal capacity of the exhaust gases, the exhaust flow rate, the sizing and type of heat exchanger, and the desired parameters over a various range of operating conditions of the cogeneration or trigeneration system — all of which need to be considered for proper and economical operation.

Many industrial processes generate large amounts of waste heat energy that simply pass out of plant stacks and into the atmosphere or are otherwise lost. Most industrial waste heat streams are liquid, gaseous, or a combination of the two and have temperatures from slightly above ambient to over 2000 degrees F. Stack exhaust losses are inherent in all fuel-fired processes and increase with the exhaust temperature and the amount of excess air the exhaust contains. At stack gas temperatures greater than 1000 degrees F, the heat going up the stack is likely to be the single biggest loss in the process. Above 1800 degrees F, stack losses will consume at least half of the total fuel input to the process. Yet, the energy that is recovered from waste heat streams could displace part or all of the energy input needs for a unit operation within a plant. Therefore, waste heat recovery offers a great opportunity to productively use this energy, reducing overall plant energy consumption and greenhouse gas emissions. 

Waste heat recovery methods used with industrial process heating operations intercept the waste gases before they leave the process, extract some of the heat they contain, and recycle that heat back to the process. 

Common methods of recovering heat include direct heat recovery to the process, recuperators/regenerators, and waste heat boilers. Unfortunately, the economic benefits of waste heat recovery do not justify the cost of these systems in every application. For example, waste heat recovery from lower temperature waste streams (e.g., hot water or low-temperature flue gas) is thermodynamically limited. Equipment fouling, occurring during the handling of “dirty” waste streams, is another barrier to more widespread use of heat recovery systems. Innovative, affordable waste heat recovery methods that are ultra-efficient, are applicable to low-temperature streams, or are suitable for use with corrosive or “dirty” wastes could expand the number of viable applications of waste heat recovery, as well as improve the performance of existing applications. 

Various Methods for Recovery of Waste Heat

Low-Temperature Waste Heat Recovery Methods – A large amount of energy in the form of medium- to low-temperature gases or low-temperature liquids (less than about 250 degrees F) is released from process heating equipment, and much of this energy is wasted. 

Conversion of Low Temperature Exhaust Waste Heat – making efficient use of the low temperature waste heat generated by prime movers such as micro-turbines, IC engines, fuel cells and other electricity producing technologies. The energy content of the waste heat must be high enough to be able to operate equipment found in cogeneration and trigeneration power and energy systems such as absorption chillers, refrigeration applications, heat amplifiers, dehumidifiers, heat pumps for hot water, turbine inlet air cooling and other similar devices. 

Conversion of Low Temperature Waste Heat into Power –The steam Rankine cycle is the principle method used for producing electric power from high temperature fluid streams. For the conversion of low temperature heat into power, the steam Rankine cycle may be a possibility, along with other known power cycles, such as the Organic Rankine Cycle. 

Small to Medium Air-Cooled Commercial Chillers – All existing commercial chillers, whether using waste heat, steam or natural gas, are water-cooled (i.e., they must be connected to cooling towers which evaporate water into the atmosphere to aid in cooling). This requirement generally limits the market to large commercial-sized units (150 tons or larger), because of the maintenance requirements for the cooling towers. Additionally, such units consume water for cooling, limiting their application in arid regions of the U.S. No suitable small-to-medium size (15 tons to 200 tons) air-cooled absorption chillers are commercially available for these U.S. climates. A small number of prototype air-cooled absorption chillers have been developed in Japan, but they use “hardware” technology that is not suited to the hotter temperatures experienced in most locations in the United States. Although developed to work with natural gas firing, these prototype air-cooled absorption chillers would also be suited to use waste heat as the fuel.  

For more information on waste heat recovery, please see our website at:  www.WasteHeatRecovery.com

Waste Heat Recovery in Cogeneration and 
Trigeneration power and energy systems

In most cogeneration and trigeneration power and energy systems, the exhaust gas from the electric generation equipment is ducted to a heat exchanger to recover the thermal energy in the gas. These heat exchangers are air-to-water heat exchangers, where the exhaust gas flows over some form of tube and fin heat exchange surface and the heat from the exhaust gas is transferred to make hot water or steam. The hot water or steam is then used to provide hot water or steam heating and/or to operate thermally activated equipment, such as an absorption chiller for cooling or a desiccant dehumidifer for dehumidification.

Many of the waste heat recovery technologies used in building co/trigeneration systems require hot water, some at moderate pressures of 15 to 150 psig. In the cases where additional steam or pressurized hot water is needed, it may be necessary to provide supplemental heat to the exhaust gas with a duct burner.

In some applications air-to-air heat exchangers can be used. In other instances, if the emissions from the generation equipment are low enough, such as is with many of the microturbine technologies, the hot exhaust gases can be mixed with make-up air and vented directly into the heating system for building heating.

In the majority of installations, a flapper damper or "diverter" is employed to vary flow across the heat transfer surfaces of the heat exchanger to maintain a specific design temperature of the hot water or steam generation rate.

In some co/trigeneration designs, the exhaust gases can be used to activate a thermal wheel or a desiccant dehumidifier. Thermal wheels use the exhaust gas to heat a wheel with a medium that absorbs the heat and then transfers the heat when the wheel is rotated into the incoming airflow.

A professional engineer should be involved in designing and sizing of the waste heat recovery section. For a proper and economical operation, the design of the heat recovery section involves consideration of many related factors, such as the thermal capacity of the exhaust gases, the exhaust flow rate, the sizing and type of heat exchanger, and the desired parameters over a various range of operating conditions of the co/trigeneration system — all of which need to be considered for proper and economical operation.

The Market and Potential for Waste Heat Recovery technologies and solutions

There are more than 500,000 smokestacks in the U.S. that are "wasting" heat, an untapped resource that can be converted to energy with Waste Heat Recovery technologies.

About 10% of these 500,000 smokestacks represent about 75% of the available wasted heat which has a stack gas exit temperature above 500 degrees F. which could generate approximately 50,000 megawatts of electricity annually and an annual market of over $75 billion in gross revenues before tax incentives and greenhouse gas emissions credits.

Waste Heat Recovery technologies represent the least cost solution which provides the greatest return on investment, than any other possible green energy technology or "carbon free energy" opportunity!

For more information on Waste Heat Recovery and Waste Heat Boilers, call/email us.

What is a "Waste Heat Recovery Boiler"?

A waste heat recovery boiler is, essentially, a boiler without any energy input. Waste heat recovery boilers are usually placed on top of a heat source or stack. Inside the waste heat recovery boiler is a series of tubes that has water inside, that is continuously circulated. The "wasted heat" is recovered on the hot side, and transferred to the water inside the tubes of the waste heat recovery boiler boiler, and then steam is generated to power a steam turbine generator, which then generates power.