Spiral Tube Heat Exchangers
The Graham Heliflow Heat Exchanger is uniquely designed and engineered to handle difficult heat transfer applications. Graham created the Heliflow to be exceptionally versatile, yielding heat transfer rates that can be more than 40% better than typical shell and tube designs. The Heliflow Heat Exchanger encompasses a spiral coil of multiple parallel tubes mounted within a casing. The case/coil construction creates a spiral flow path providing true counterflow. Each application is specially engineered for optimal thermal and hydraulic requirements balance, resulting in maximum heat transfer efficiency. High pressure, specialized materials, cyclic operation, temperature extremes, and other conditions can be handled easily. The Graham Heliflow Heat Exchanger has years of proven service in thousands of applications worldwide, with high-quality performance always guaranteed.
The many advantages of the unique Graham Heliflow make it an efficient heat exchanger for a wide range of applications; some of which include:
- High pressure
- Natural gas heaters
- Vent condensers
- Mechanical seal coolers
- Compressor inter/aftercoolers
- Supercritical fluid
- Feedwater preheaters
- Lethal service
- Steam or process fluid vaporizers
- Boiler or process sample coolers
- Hot water heaters
- High temperature
- Freeze condensers
- Hydraulic/lube oil coolers
The Graham Heliflow is ideally suited for applications with a liquid-to-liquid service requiring a heat exchanger.
When designing the exchanger, the “dirty” fluid should be on the shell side of the unit. The Heliflow makes shell-side cleaning easy. Cleaning can be done in place without breaking shell-side or tube-side pipe connections. The flow pattern is 100% countercurrent, maximizing the temperature differential and thermal efficiency.
Graham has conducted extensive research and development in the area of cryogenic vaporizers. Our research and many years of proven experience in this area confirm that the Heliflow heat exchanger is excellent for cryogenic applications. The unique tube coil of the Heliflow can easily accommodate the large temperature differentials typical in cryogenic units.
Heliflow Heat Exchangers often use cryogenic fluids as the cooling medium; alternately, Heliflows can vaporize fluids, such as N2, O2, CO2, or other fluids. For information on this subject, refer to the Graham article titled Convective flow boiling in coiled tubes. Convective flow boiling in coiled tubes.
High pressure applications are another way to utilize the Heliflow Heat Exchanger. The tubeside of the exchanger does not rely on gaskets for sealing, and can be designed to 15,000 psig. A key advantage that a Heliflow offers is that it has no flat sided pressure bearing surfaces that quickly become thick as design pressure increases.
A Heliflow uses tubing and pipe to contain the tubeside’s usually high operating pressure fluid.
The shellside of the unit can be rated for pressures up to 5,000 psig.
To read more on the subject, go to: Heliflow High Pressure Applications.pdf
Boiler blowdown and process sample coolers are perfect applications for a Heliflow heat exchanger. The compact size of the Heliflow fits into tight spaces. Also, the Heliflow design can withstand the cyclic nature of blowdown service.
Natural gas heaters
When natural gas is passed through a pressure reducing station, it decreases in temperature. The compact Heliflow design is often used to increase the temperature of the natural gas.
Heliflow Heat Exchanger technology is at the heart of Graham’s vent condensers.
Vent condensers are often used on storage tanks to reclaim products contained in the tank and control the harmful emissions that escape from the tank to atmosphere. During the day, the sun heats the fluid in the tank. The increase in the system’s temperature will cause the vapors in the tank to expand and increase vaporization of the volatile components as their vapor pressures increase. By installing a vent condenser on the vessel, the condensable vapors are reclaimed and refluxed back into the storage tank.
In addition to the venting caused by temperature changes, vapors are exhausted to atmosphere as the tank is filled. The vent condenser experiences the greatest thermal duty when the tank is being filled. The heat exchanger, therefore, should be sized based on the filling case.
Graham has taken the lead in reducing VOC (volatile organic compound) emissions with our design of specialized vent condensers. These units often are used to recover valuable product and reduce the load on downstream pollution control equipment at the same time.
Three styles are available for your choosing:
- No casing required, most economical choice
- Typically used for new vessels
- Drop tube can be supplied to reflux condensate below liquid level
- Fits inside a flanged vessel connection
- Typically used on existing vessels
- Does not require additional supporting structure
- Mounts on top of flanged vessel connection
- Corrosive fluid can be placed on the tubeside
- Casing can be lower cost material
- Permits sub-cooling of the condensate
Mechanical seal coolers
Keeping the mechanical seal faces cool is extremely important in extending the operating life of mechanical seals. The unique design of the Graham Heliflow facilitates superior cooling of the seal flush fluid as compared to traditional mechanical seal coolers.
Heliflow seal coolers can be fitted with vent connections which enable the units to meet the venting and draining requirements of API 682. In addition, Heliflow seal coolers have the ability to thermosiphon in the event of a pumping ring failure.
API flush plans 21 or 23 are the common arrangements for configuring mechanical seal cooling systems. In Plan 21, the product from the pump discharge is circulated through a valve or orifice and then flows through a Heliflow seal cooler where it is cooled before returning to the mechanical seals. In API Plan 23, the product is recirculated from the stuffing box through the Heliflow and then back to the mechanical seal.
Standard models are available in 316 stainless steel tubeside and cast iron shell. Options include 304 stainless steel, titanium, 70/30 cu.ni. tubes, 316 stainless steel and cast steel shell materials. Units can also be constructed to ASME Section VIII, Division 1 Code if desired.
Sizing software is available from Graham to assist in selecting units for both API Plans 21 and 23.
API 682 compliant units:
Standard Heliflow units do not conform with the tubing recommendations of API 682, however, specially designed units are available, which include 3/4″ diameter x .095″ wall thickness tubes to provide complete compliance with the standard.
To read more on seal coolers, see: Pump Seal Coolers
Heliflow Heat Exchangers are preferred for high pressure service, and are often used as inter and aftercoolers to cool the gases handled by reciprocating type compressors. Typical design pressure is 2500-5000 psig, however, units designed for up to 15,000 psig are available.
Graham has extensive experience in engineering, design, and fabrication of units for compressor service.
Supercritical water oxidation (SCWO) is a cutting edge technology developed for the treatment of hazardous waste solutions. This method uses high pressure, high temperature water at its supercritical state of 3200 psig and 705 degrees F. During this process, oxygen and the supercritical water are injected into the waste stream. The waste contaminants are oxidized, transforming them into carbon dioxide and other harmless substances.
This process is cost competitive and more environmentally friendly than traditional disposal methods, such as landfill or incineration.
Specially designed Heliflow Heat Exchangers with spherical casings are used to withstand the high operating pressures and temperatures required. These units are used to cool the reactor effluent, to generate steam, as a feed interchanger, and as sample coolers.
To read more on supercritical fluid applications, see: Supercritical Fluids
Heliflow Heat Exchangers can save energy as heat recovery economizers. Waste heat is recovered and utilized to preheat incoming make-up water that is used in boilers or for other applications.
Specially designed Heliflow Heat Exchangers are available for use when handling lethal liquids or vapors. These units are built to strict manufacturing, welding, and quality control specifications and include specially developed features to provide confidence when handling lethal fluids.
Steam or process fluid vaporizers
The Heliflow Heat Exchanger design is often used to provide a compact vaporizer. The coiled tube bundle promotes nucleate boiling, and can easily handle the stresses caused by thermal expansion and cycling. Steam or other high temperature sources are often used to vaporize nitrogen, oxygen, carbon dioxide, hydrogen, methane, ethylene, various hydrocarbons, and many other fluids. Vaporizing can be achieved either shellside or tubeside according to process requirements.
Boiler or process sample coolers
The compact footprint of the Heliflow Heat Exchanger, along with its ability to handle frequent cycling and wide temperature differentials make this unit ideal for use in sample cooler applications.
Hot water heaters
Heliflow Heat Exchangers can heat water using steam or high temperature hot water (or other fluids) as the energy source. When control of the water temperature is important, temperature control valves are often used with the Heliflow design.
If the water flow rate varies, and outlet temperature must be controlled, Graham offers our packaged MicroMix II instantaneous, steam-fired, hot water heaters.
A benefit of Heliflow Heat Exchangers at higher temperatures is the ability of the coil to flex as it is heated. As the tubes are heated, they grow due to thermal expansion. Because the Heliflow bundle is free to move, the units can undergo many years of cyclic operation without problem.
A major drawback for many other types of exchangers is reduced operating life when working at higher temperatures, or the exchanger must include expensive expansion joints. A Heliflow Heat Exchanger is the best choice for high temperature applications.
Freeze condensers fall into two categories; the first includes vapors that condense, then freeze in the heat exchanger. The second category typically includes nonfreezing condensables mixed with water vapor or another component, which does freeze.
Both applications are similar in that the objective is to condense and remove from the vent stream as much of the vapor component as possible. The most effective method is to cool the vapor below its freezing point, however, once a component begins to freeze, the heat transfer rate is gradually decreased. To obtain the best efficiency, often two parallel units are used. One unit operates, while the other undergoes a thaw cycle.
Graham is uniquely experienced in the field of freeze condenser technology. Our Heliflow Heat Exchangers can be provided based on system requirements. Years of experience and numerous research projects enable Graham to provide “Engineering Answers” tailored to specific applications.
The tubes in the Heliflow are arranged in parallel, starting with an inlet manifold on one end, and terminating at an outlet manifold on the opposite end. The tube bundle is wound into a helical pattern. This coiled construction creates a spiral flow path for the fluid inside the coil.
Each tube is in close contact with the tube above and below it. The coiled tube bundle is fit into a two-piece casing. When the casing is tightened, it is designed to slightly compress the tubes. Because of the tight fit, the shellside fluid is forced to circulate in a spiral pattern created by the open spaces between the coils
Advantages of Graham Heliflow Spiral Tube Heat Exchangers
- Higher efficiency
- Easy to maintain
- Accommodates pressures up to 15,000 psig
- High reliability
- Code compliant
- Easily customized
- Low flow rates
- Compact design
- Withstands 500 deg. F temperature difference between fluids
- Varied material choices