The Guided Rotor Compressor

A Compressor for the 21st Century

Combined Heat & Power, Inc.

This Technology is for Sale

Please contact Ned Daffan

Last Revision: October 3, 2013

Latest News

Combined Heat & Power, Inc. continues to introduce new Guided Rotor Compressor (GRC) models to expand its product range. In 2010, Combined Heat & Power, Inc. introduced and shipped a high pressure version of the M500 family of compressors. This new model, named the M500HP, is rated for a Maximum Allowed Working Pressure (MAWP) of 1200 psig. This first production example will be used in a proprietary high pressure air drilling system.

Combined Heat & Power, Inc. is also proud to introduce the new M450 series, a high pressure (1000 psig) compressor series designed t be coupled to a twin screw booster stage, or as a stand alone Guided Rotor Compressor.

Combined Heat & Power, Inc. also offers high pressure heat exchangers which are designed to complement multistage high pressure versions of the Guided Rotor Compressor. The heat exchanger design is also intended to provide a high pressure oil cooler to the general industrial marketplace. The first production run of heat exchangers is rated to 1,200 psig MAWP, and is sized to reject 300 hp equivalent of heat if the working fluid is 100% mineral oil, and 150 hp if the working fluid is a 50%/50% mixture of oil and natural gas. This compact design heat exchanger is hydro tested and coded for its working pressure, and allows significant flexibility in packaging. Additional sizes are available, as well as versions that include compressor and engine cooling functions in one heat exchanger assembly.

Table of Contents:

Detailed Description and Defining Geometry
Mechanical Attributes
Performance Attributes
Production Models
Compression Of Gases Other Than Natural Gas


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Combined Heat & Power, Inc. is pleased to announce that a new and revolutionary natural gas compressor is commercially available for a wide range of wellhead and gas gathering production applications, coal-bed methane applications, landfill/digester gas applications and fuel gas booster service. This new compressor, referred to as the Guided Rotor Compressor, or GRC, provides new levels of performance, reliability and operating flexibility for natural gas production and utilization operations. The GRC provides application and operating flexibility that exceeds the performance levels of traditional reciprocating and twin screw compressors, as well as scroll, vane and liquid ring compressors.

The GRC is a rotary positive displacement device, which is based upon an envoluted trochoid geometry. The device represents a new family of rotary compressors. The GRC is not a Wankel device and there is no mechanical design relationship between the GRC and reciprocating, twin screw, single screw, vane or scroll designs. The compression volume is defined by a trochoidal surface within a casing, or housing, and a rotating rotor mounted on an eccentric drive shaft. Depending upon configuration, three to four compression volumes are defined by a rotor/housing pair, thereby providing 12 to 20 compression processes for each full rotation of the rotor. One or more rotors are available for single stage, and multistage operation.

Application benefits include very wide inlet pressure and discharge pressure capability, high efficiency, compact compressor footprint for single and multistage configurations, wide off-design operating potential without efficiency degradation, high reliability and longevity, low part count (no compressor valves, no piston rings, no linear strip seals), and reduced system packaging cost.

Detailed Description and Defining Geometry

The Guided Rotor Compressor (GRC) is a rotary positive displacement device. Other common rotary positive displacement compressors are the; twin (helical) screw, rotary lobe, rotary vane, scroll, rolling piston, single (globoid) screw and liquid ring compressors. The other major positive displacement compressor type is the reciprocating compressor, which utilizes the "back and forth" reversing motion of pistons or diaphragms, rather than rotary motion, to achieve volume reduction.

The GRC is an envoluted trochoid device, which utilizes a parallel trochoid curve to define its basic compression volume. The historic Wankel engine (and compressor variant) utilized the theoretical trochoid rather than the envolute. The GRC also utilizes a cylindrical seal rather than a linear seal of the Wankel. It is the combination of the envoluted trochoid and the cylindrical seal, along with proprietary geometric proportions, which allow the GRC to function and provide superior operating characteristics.

The GRC is simple in configuration and construction. A single rotor compressor assembly is comprised of; a trochoidal housing, a rotor, roller seals, suction side plate, discharge side plate, crankshaft, rotor bearing, main bearings, end covers, and a ceramic face seal. The compressor is modular in construction and can be configured as a multi-rotor and multistage assembly, while separate compressor assemblies can be close coupled together to achieve further product line expansion. The Guided Rotor compressor does not utilize nested timing gears and does not require speed increasers to achieve cost effective delivery volumes.

Current production designs are liquid lubricated; employing fluid such as mineral oil, synthetic oil, ATF and glycol. Concept designs have been developed for lubricant free GRC's, although full scale design and prototyping is not planned for the near term. Additional market segments can be addressed since the Guided Rotor device can operate as a positive displacement expander or as a combined compressor/expander.

The key geometric descriptor for the GRC is the Eccentric (e). This one variable, along with other elective considerations, virtually defines a particular GRC design. The Eccentricity is approximately equivalent to the "stroke" of a reciprocating compressor, in terms of performance definition. Those familiar with the GRC, use the Eccentricity as the designator for a core design series. The Eccentricity does not, however, describe the many variables available within a core design. These are defined by secondary geometric selections.

Secondary geometric information includes; number of rotors, number of stages, number of rotors per stage, number of lobes (n=number of lobes, n+1=number of rotor faces), and rotor width(s). Performance or design operating considerations include; rpm, suction pressure, discharge pressure, flowrate.

Each individual multirotor GRC design can have different Eccentricities (e) for each rotor, as well as different rotor dimensions, number of lobes and utilize different gases for each rotor. The GRC can also be close coupled directly to another compressor type such as a reciprocating compressor. The only constant is shaft speed (rpm).

Mechanical Attributes

Mechanical attributes of the Guided Rotor Compressor (GRC) encompass the following characteristics:

Various models of the Guided Rotor Compressor (GRC) are available as either a four sided rotor, three lobe configuration or as a five sided rotor, four lobe configuration. For each rotor rotation, twelve or twenty compression processes occur respectively. As such, the GRC is generally smaller in overall size than comparable reciprocating compressors. On the basis of actual rotor speed, the GRC is also significantly smaller than twin screw compressors, although in practice, the majority of twin screw compressors utilize speed increasers to achieve high volume flowrates and apparent small size.

The GRC is exceptionally simple in construction. A typical single rotor configuration is assembled from less than 20 components, not counting fasteners. A comparable single cylinder reciprocating compressor is comprised of at least double the number of parts. Reciprocating parts are also complex in design and more fragile. The GRC components are simple in configuration and significantly more robust in cross-section and construction.

Generally, GRC based compression systems for wellhead and gas gathering applications can be 40% smaller than comparable reciprocating systems, and 25% smaller than twin screw based systems. Packaging costs are significantly lower due to low vibration levels and a small compressor footprint. GRC assemblies can be configured to accept piping connections at regular circumferential positions during compressor assembly, thereby allowing the system designer exceptional flexibility.

Compressor valves and piston rod packings are completely eliminated, thereby avoiding costs associated with these component failures and resultant downtime. The GRC utilizes simple cylindrical rollers that are exceptionally robust and long lasting to seal between compression volumes. Experience to date indicates that roller life is at least two years, with no performance degradation. The only other wear component is a ceramic-on-carbon face seal for the drive shaft. This face seal has proven to be very reliable and long lived.

Performance Attributes

Performance Attributes of the Guided Rotor Compressor (GRC) are:

Recent tests of a 20 hp GRC operating on air with an ambient inlet pressure, revealed measured adiabatic efficiencies ranging between 75% and 88%, at pressure ratios ranging from 2.8 to 4.6. This testing was competed by a third party, experienced in the performance measurement of a wide range of rotating equipment.

Laboratory and field testing experience shows that off-design performance is relatively flat as a function of rpm. This performance attribute allows significant flexibility with regard to installation longevity under changing field conditions.

Because liquid lubricant is introduced and is present within the compression volume, the GRC experiences a degree of isothermal cooling during compression. As a result, discharge temperatures experienced with the GRC are significantly lower than for comparable reciprocating compressors impacting the size and cost of installed heat exchangers.


Packaging the Guided Rotor Compressor provides significant opportunities to reduce the cost and complexity of compression systems. For a given performance level, the GRC is more compact, highly flexible for multistaging, provides numerous options for piping connections and transfers no shaking forces to the skid and foundation. The structural elements of the support skid can be lighter and significantly smaller than comparable reciprocating compressor systems.

The package on the left utilizes a GRC three stage natural gas wellhead or gas gathering compressor (Model No. 410-108) driven by a 150 hp engine drive mounted upon a simplified fabricated support skid. This package design represents one of the standardized designs developed by Combined Heat & Power, Inc. for natural gas production applications. For the larger Model 500 family of derivative GRC designs, the package layout and detail design for natural gas service is identical, whether the compressor is a single stage or a four stage assembly; differing only in driver horsepower, number and size of radiators and separators, and overall skid length. A high level of standardization is exhibited throughout the product range, resulting in lower costs, lower parts inventory and higher maintenance efficiency.

The package nearing completion above represents a highly standardized package suitable for application anywhere between a 0 psig to 125 psig inlet pressure and 250 psig discharge pressure, while delivering 100 mcfd to 1000 mcfd respectively, at less than 60 hp. The installed GRC is a Model 410-102, which is a two rotor, two stage configuration. This standard package design is suitable for Models 312, 350 and 410 single stage or two stage GRCs' driven by natural gas engines or electrical motors. The package is designed for high reliability, wide applicability, ease of access and maintenance and a small footprint (10' L x 5' W). The basic layout is also utilized for higher horsepower systems and for higher discharge pressure systems.

Production Models

Combined Heat & Power, Inc. has designed and developed a broad natural gas compressor product line ranging between 10 to 5000 horsepower. This product line is differentiated and identified by Combined Heat & Power, Inc. by a model number related to the Eccentricity followed by a three digit suffix which identifies the assembly configuration. For example, the Model 410-102 is a compressor assembly utilizing an Eccentricity of 0.410", with the suffix -102 further identifying the assembly as a two stage configuration. The Model 1000 family of compressors utilize an Eccentricity of 1.000". The GRC product line potential extends from numerous marginal wellhead applications, through larger gas gathering, enhanced oil recovery applications within the natural gas production markets, as well as for the landfill/digester gas recovery markets. The GRC product line is also very suited for distributed generation fuel gas booster applications utilizing gas turbines and reciprocating engines.

For natural gas production applications, Combined Heat & Power, Inc. has designed a series of standardized compression packages suitable for a broad array of field appplications. Further information and quotations are available by contacting Combined Heat & Power, Inc., or its authorized distributor/packagers.

There are twelve (12) core designs in the GRC family:

Type NumberEccentricityMax Suction PMAWP
Model 2500.250"250 psig350 psig
Model 2750.275"250 psig350 psig
Model 3120.3125"250 psig350 psig
Model 3500.350"600 psig1300 psig
Model 350HP0.350"600 psig1300 psig
Model 3750.375"250 psig400 psig
Model 4100.410"250 psig450 psig
Model 5000.500"250 psig600 psig
Model 500HP0.500"250 psig1200 psig
Model 7000.700"600 psig800 psig
Model 7500.750"600 psig550 psig
Model 10001.000"600 psig1200 psig
Model 14001.400"600 psig1200 psig

Current inlet pressure maximums are defined by the drive shaft face seal design. The face seal is a simple and very reliable spring loaded carbon on ceramic design, suitable for an inlet pressure of 250 psig. If higher pressures are required, balanced face seal selections are available.

There are currently one hundred seventy eight (178) derivative assemblies based upon the above core designs. There are currently two (2) or more rotor widths for each core group. Future market requirements may dictate additional rotor widths and additional or modified aseembly configurations. Assembly derivatives, which are identified as "coupled" designs, are modular combinations of dual and/or single rotor assemblies, of identical or differing eccentricities, coupled together.

If additional rotor widths and differing eccentricities are applied, the number of possible combinations to address customer needs increases rapidly. It should be apparent, that although the number of assemblies increases dramatically, the number of specialized, one of a kind components remains low, thereby increasing production efficiency and economics.

The rpm range of the GRC product line is generally set between 900 rpm and 2,400 rpm, with the nominal at 1,800 rpm. The exceptions are the Model 700 which is currently limited to 1800 rpm, the Model 1000 which is currently limited to 1200 rpm and the Model 1400 which is currently limited to 900 rpm. Laboratory test runs, on prototypes, exceeded this recommended range, however these limits are currently selected for long term reliability, and to match available drivers. Virtually all commercial field experience is at 900 to 1,800 rpm, due primarily to driver selections.

The GRC product range are all oil lubricated designs, using; mineral oil, synthetic oil, ATF and process liquids. Combined Heat & Power, Inc. has approved GRC Models 250, 275, 312, 410 and 500 for glycol and glycol/water lubricated operation. Please consult with Combined Heat & Power, Inc. since horsepower limits are derated with these lubricants.

Currently, variable geometry apparatus for capacity unloading and variable pressure ratio control are not included in the GRC product range. Experience has shown that performance variation is minimal for GRC's at varying pressure ratios, and variable capacity can be economically achieved by external means. As such, the added complexity of variable geometry is not generally needed in conventional applications. If market conditions require variable geometry, Combined Heat & Power, Inc. will introduce variable geometry options.

With fixed suction and discharge porting, pressure ratio per stage is optimized between 2.5:1 and 3.0:1. Individual GRC assemblies can be optimized for other pressure ratios, if required and justified. Combined Heat & Power, Inc. is currently limiting maximum continuous pressure ratio per stage to 5:1. This self-imposed limit is to maximize thermodynamic and volumetric efficiency, and because multistaging the GRC is exceptionally easy. Higher pressure ratios are however possible and limited laboratory and field testing shows that there is potential to increase this imposed limit within future compressor generations.

Current Performance Limits for the GRC Product Line are:

 Model 250Model 275Model 312Model 350
MAWP350 psig350 psig350 psig1300 psig
Max Suction Pressure (Face Seal Limitation)250 psig250 psig250 psig600 psig
Delta P for 1st Stage Rotor125 psi110 psi120 psi250 psi
Delta P for 2nd Stage Rotor180 psi160 psi170 psi400 psi
Total Delta P for Two Stage Assembly305 psi270 psi290 psi650 psi
Max Pressure Ratio per Stage(Consult CHP, Inc.)(Consult CHP,Inc.)(Consult CHP, Inc.)(Consult CHP, Inc.)
Max Horsepower per Assembly30 hp40 hp40 hp150 hp

 Model 350HPModel 375Model 410Model 500
MAWP1300 psig400 psig450 psig600 psig
Max Suction Pressure (Face Seal Limitation)1000 psig250 psig250 psig600 psig
Delta P for 1st Stage Rotor400 psi163 psi165 psi180 psi
Delta P for 2nd Stage Rotor400 psi235 psi235 psi250 psi
Total Delta P for Two Stage Assembly800 psi400 psi400 psi430 psi
Max Pressure Ratio per Stage(Consult CHP, Inc.)(Consult CHP,Inc.)(Consult CHP, Inc.)(Consult CHP, Inc.)
Max Horsepower per Assembly300 hp150 hp175 hp225 hp

550 psig
 Model 500HPModel 700Model 750Model 1000
MAWP1200 psig800 psigN/A1200 psig
Max Suction Pressure (Face Seal Limitation)250 psig250 psig250 psig600 psig
Delta P for 1st Stage Rotor600 psi350 psi350 psi350 psi
Delta P for 2nd Stage Rotor900 psi400 psi400 psi550 psi
Total Delta P for Two Stage Assembly1500 psi650 hp650 psi900 psi
Max Pressure Ratio per Stage(Consult CHP, Inc.)(Consult CHP, Inc.)(Consult CHP, Inc.(Consult CHP, Inc.)
Max Horsepower per Assembly550 hp600 hp600 hp1940 hp

 Model 1400
MAWP1200 psig
Max Suction Pressure (Face Seal Limitation)600 psig
Delta P for 1st Stage Rotor500 psi
Delta P for 2nd Stage Rotor800 psi
Total Delta P for Two Stage Assembly1300 psi
Max Pressure Ratio per Stage(Consult CHP, Inc.)
Max Horsepower per Assembly5000 hp

Compression Of Gases Other Than Natural Gas

The GRC can be applied to a wide range of gases. For existing production assembly numbers, suction and discharge port locations are optimized for the thermophysical properties of natural gas. For optimized operation with other gases or gas mixtures, such as Helium, Hydrogen, air or process gas streams, different port locations are defined and new performance envelopes are developed. In addition to relocated and resized suction and discharge porting, specialized considerations such as material selections, face seal design and rotor/housing width selections are also reviewed for the gas and intended application. If required, production GRC models can be manufactured in Stainless Steel. Please contact Combined Heat & Power, Inc. for further details.


Early commercial applications for the Guided Rotor Compressor (GRC) have been in marginal wellhead, larger wellhead, gas gathering service and in fuel gas booster service for micro turbine based distributed generation. Short term marketing and sales efforts center upon marginal wellhead compression, gas gathering, enhanced oil & gas recovery service and landfill/digester gas recovery. As unit field population increases, additional GRC models will be introduced into broader market segments.

The GRC pictured on the left is providing gas gathering service in Western New York. The system draws from 17 wellheads and delivers natural gas to a sales line and to a food processing plant. As of December 2009, the compressor has operated successfully for over 49,000 hrs. At approximately 5,000 hours, the control solenoid for lubricant oil supply failed, causing the compressor to run intermittently without lubrication for an estimated 25 to 30 hours. Upon discovery of this system failure, the compressor was disassembled and inspected for damage. The guiding rollers were found to be slightly scuffed, but fully functional and not in need of replacement. The rollers were however replaced to allow testing of another set of rollers based on a different design. These alternate rollers have operated for over 37,000 hours without performance degradation, the equivalent of 4.2 years of 24/7 operation. The incident described would have quickly caused a failure in a competing compressor type.

The GRC has also been successfully applied in supplying natural gas to a large system of microturbines in an innovative distributed generation installation. The installation pictured on the right is part of the world's largest utility independent micro turbine installation powering an industrial plant. Of the three compressors pictured, 1.5 compressors were required to provide full fuel load to twenty (20) micro turbines, each capable of producing 30 kw each. The balance of the compressors provided a level of redundancy.

During the initial start-up phase of this micro turbine installation, the amount of natural gas required limited compressor operation to a single unit operating 7 seconds on, 9 seconds off. During the system commissioning period, this single compressor experienced nearly 30,000 stop/start cycles without performance degradation. The drive systems were not equiped with soft starts or VFD's. On another occasion, one compressor module of the three pictured was rewired inadvertantly for reverse rotation, with the lubricant oil control bypassed. This compressor operated for some hours in the reverse direction and without lubricant flow, again without ultimate performance degradation, once again demonstrating the ruggedness of the GRC.

The following provides a quick summary of the potential markets and uses of the Guided Rotor Compressor:

Natural Gas/Oil Production Fuel Gas Boost Environmental Compression Hydrogen Refueling and Infrastructure Development Process Gas Compression Refrigeration Utility Local Line Pressure Maintenance CNG/LNG Storage and Refueling Automotive and Truck Air Compression

This page is Copyright © 2013, Combined Heat & Power, Inc.

Combined Heat & Power, Inc.
Please contact Ned Daffan
Phone: (703) 328-7203