An Illinois-based organisation dedicated to researchdevelopment and training for the natural gas industry has developed a new industrial steam generation system that provides increased efficiencyreduced emissions and lower fuel costs.
Gas Technology Institute (GTI) has teamed with Cleaver-Brooks-a leader in packaged boilers for industrialinstitutionaland commercial applications-to focus efforts on bringing technological advances to the marketplace.
Smaller footprint
Now in field demonstration at Specification Rubber Products in Alabamathe advanced
gas-fired boiler-dubbed the ‘super boiler’ by its sponsors-has shown significant performance improvements over alternative technologies.
In additionthe boiler has a 40percent smaller footprint and half the weight of conventional boilers.
A critical part of the system design is its ability to meet future nitrogen oxide (NOx) emissions regulations without the need for expensive post-combustion flue-gas treatments.
“The development of this technology is being driven primarily by rising energy prices combined with increasingly stringent emissions regulations” explains GTI’s Rick KnightR&D managerPower Generation.
“Todayindustrymanufacturersand the government are teaming with GTI to develop cleanermore efficient ways to use fossil fuels.”
Project sponsors
Sponsors for the super boiler project include the US Department of EnergyCleaver-BrooksGas Research InstituteUtilisation Technology Development NFPGTI’s Sustaining Membership Programthe Southern California Gas Companythe California Energy Commissionthe California Air Resource Boardand the South Coast Air Quality Management District.
Researchers note that while steam boilers account for about 35percent of industrial energy useabout 80percent of the currently operating steam boilers are more than 25 years old. Energy efficiency for gas-fired boilers is typically in the 75–83percent rangeand uncontrolled NOx emissions are about
70 parts per million.
While NOx reduction measures are readily availablethey generally increase capital and operating costs and consume additional energy.
The goal for the super boiler is to achieve
fuel-to-steam efficiency greater than 94percent while maintaining NOx and carbon monoxide levels below five parts per million.
“In the industrial sectorboilers are the single largest energy consumer” says Knight“particularly in papersteelchemicaland food industries. However100-year-old technology is still in use.
“Improvements in efficiency and emissions performance are needed to maintain US industry competitiveness and help meet urgent challenges for better air quality and reduced greenhouse gas emissions.”
In 2005GTI and Cleaver-Brooks designed and fabricated a 12millionBtu/h (300hp) prototype boiler system that includes the boilerburnerfancontrolsfuel trainand heat-recovery system.
To achieve low emissionsresearchers are using a patented combustion concept developed by GTI and this is derived from the forced internal recirculation burner.
Heat recovery systems
To achieve high efficiencya heat-recovery system was developed and patented that employs a novel transport membrane condenser (TMC)a humidifying air heater (HAH)and ultra-compact dual economisers.
“The prototype super boiler has been laboratory tested with good results” says Knight. “We have already confirmed that the first 300hp
field-demonstration unit can achieve greater than 94percent fuel-to-steam efficiencywhich will save the facility more than US$50000 annually in fuel (based on US$12 per million Btu).”
The super boiler consists of two main parts: the boiler and the heat recovery system. The boiler employs a split-combustion section designed to address the low-emission goalalong with enhanced heat transfer innovations from Cleaver-Brooks to achieve a very compact design.
The heat recovery system is designed to recover most of the remaining heat in the flue gas coming out from the boilerincluding the latent heat associated with water vapourwhich accounts for two-thirds of the waste heat from natural gas combustion.
Two ultra-compacthigh-efficiency economisers are incorporated into the system to recover sensible heat of the total flue-gas stream before it enters the TMC.
In that devicewater vapour passes selectively through a nanoporous ceramic membranegiving up additional sensible heat and all of its latent heat to the boiler feed water.
The HAH plays a critical role in managing water temperatures in applications that return and re-use a major portion of the condensate from their steam system.
The HAH also conditions the incoming combustion air to further reduce NOx emissions in the boiler.
“A unique feature of this system is the ability to recover flue-gas moisture for use as additional boiler feed water” says Knight. “This reduces makeup-water requirements and recovers as much waste energy as possible.”
Field demonstration
A field demonstration of a second prototype unit is planned for later this year at a juice bottling plant in OntarioCaliforniawith an additional demonstration of the heat-recovery system retrofitted to a conventional boiler scheduled for installation at a manufacturing site in mid-2007.
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