GTI has more than six decades of experience in developing and evaluating advanced combustion systems for use in residential, commercial, industrial and power generation markets. In this time of volatile energy prices, it is providing opportunities for energy-use markets to more flexibly address currently rising gas prices by using more efficient gas equipment already developed or under development. GTI researchers also are working to reduce the environmental impact associated with the use of such equipment.
Most of GTI's combustion technology development is performed in its 11,000 ft2 state-of-the-art Commercial/Industrial Combustion Laboratory in conjunction with leading manufacturers and end-users in competitively secured contracts from funding entities such as U.S. Dept. of Energy (DOE; www.energy.gov), California Energy Commission (CEC; www.energy.ca.gov), and the natural gas industry. Typical projects involve bench-scale and pilot-scale development testing, followed by field demonstrations and technology transfer to commercialization partners through licensing arrangements.
"For more than 60 years, GTI's combustion program has been providing solutions for the large commercial and industrial sector," says Hamid Abbasi, Executive Director of GTI's Energy Utilization Center. "Over time, we have changed our program to address the changing needs of the industry, and today, we are focused on near-term product development. The breadth and flexibility of our laboratory gives us the capability to meet the combustion R&D needs of virtually any customer."
History of commercial success
Several examples illustrate the commercial successes from GTI's combustion program. Support for these developments has primarily come from DOE's Industrial Technology Program (ITP) and GTI's Gas Industry Programs.
Forced internal recirculation (FIR) burner
GTI's low-emissions FIR burner (Fig. 1) can be used in a wide range of industrial boiler applications for producing paper, chemicals, petroleum products, food and steel. The burner technology demonstrates low nitrogen oxides (NOx) and carbon monoxide (CO) emissions from natural gas combustion without any energy efficiency penalty.
NOx emissions reduction is accomplished without the use of external flue gas recirculation (FGR), special control techniques, complex internal moving parts, high excess air, or special air handling, which typically are used with other methods. The FIR burner uses a GTI-patented method that uses a recirculation insert in the combustion chamber adjacent to the burner face to promote internal gas recirculation. The recirculation insert also provides a flame attachment point to increase the flame stability.
The simplicity of the FIR design is an important characteristic. The FIR burner can be operated with standard controls and flame safeguards used with conventional burners. This makes the burner attractive for the retrofit market because the customer is not required to buy any special equipment or controls to replace their existing burner.
Some alternative NOx reduction techniques require complex internal moving parts that need special linkage arrangements or special electronic control techniques to accomplish the movement.
Another advantage to the FIR design is the low excess air requirements to operate it as opposed to high excess air levels required with other NOx reduction technologies. Disadvantages of high excess air use are higher operating costs due to increased electrical energy usage to supply the extra air and decreased boiler efficiency.
FIR burner technology is licensed to Johnston Boiler Co. (for firetube boiler applications) and to Coen Company Inc., (for packaged watertube boiler applications). In addition, a Memorandum of Understanding was signed with Hamworthy Peabody Combustion Inc. (for application in field-erected boilers in the steel industry) pending a successful field demonstration in 2004. Southern California Gas Co. (www.socalgas.com) provided additional funding to develop this technology.
TI developed METHANE de-NOX(r), a combustion modification process that significantly reduces stoker NOx emissions, while increasing boiler performance and enhancing combustion of problem fuels such as coal, wood-waste and sludge. The process is aimed at boiler operators seeking to minimize total cost to reduce emissions while increasing boiler energy performance.
In the process, natural gas together with recirculated flue gases are injected above the combustion grate to create an oxygen-deficient zone. Direct injection of natural gas into the combustion zone reduces the availability of oxygen that could result in NOx formation. Under these conditions, a significant part of NOx precursors decompose and react, forming molecular nitrogen rather than NOx. Tests confirm the added heat release from natural-gas combustion above the stoker grate stabilizes the firing of solid fuel, which improves combustion of difficult-to-burn waste fuels such as those with a high moisture content.
With METHANE de-NOX, overfire air (OFA) is injected at a higher elevation in the furnace to allow sufficient residence time to complete the reburn reactions. Adding OFA burns out the remaining combustibles and CO in the furnace gases.
GTI is actively involved in technology transfer and deployment with its commercial licensee, ESA Environmental Solutions (www.energysystemsassoc.com). Working closely with end-users and partners, GTI continues to participate in testing, modeling and design for commercial applications.
Oxygen-enriched air staging (OEAS)
TI's OEAS process reduces NOx by 50-70% in glass furnaces with no negative impact on glass quality. Tests on glass melters in the field show that OEAS is by far the most cost-effective method in terms of dollar-per-ton spent to decrease NOx emissions in this application.
With OEAS, all combustion occurs inside the furnace over the surface of the molten glass, minimizing energy-cost impacts for NOx control. As part of the process, the amount of combustion air through the firing ports is reduced to decrease the oxygen available in the flame's high-temperature zone in a first combustion stage. This reduces NOx formation, but leads to higher CO and unburned hydrocarbon levels. Air or oxygen-enriched air is then injected into the furnace near the exit port(s) to complete combustion in a second stage within the furnace.
The technology has been successfully retrofitted on more than 12 endport and sideport container glass furnaces in the U.S., Europe and South America. NOx emissions are reduced between 50-70% on endport furnaces. The first application of OEAS to a sideport furnace (300-tpd) decreased NOx by 40% to below 2.5 lb/ton. To put into perspective, Southern California currently limits NOx emissions from all container glass tanks to 4 lb/ton and is considering even more stringent regulations.
The OEAS system has been operating continuously for six years. OEAS systems subsequently installed on several 320-tpd sideport furnaces reduced NOx by as much as 70%. OEAS technology is licensed to Combustion Tec (glass division of Eclipse Combustion Inc.; www.eclipsenet.com), who is marketing OEAS for endport and sideport furnaces used in multiple glass industry segments, including container, flat and sodium silicate glass. GTI is working with Eclipse to apply OEAS NOx reduction technology to other high-temperature furnaces in the steel, ceramics, metals processing and other industries. Southern California Gas Co. provided additional funding for this work.
High-luminosity oxygen/gas burner
Oxygen/natural gas combustion offers benefits for high-temperature materials processing including reduced NOx emissions, better furnace control, a compact furnace system (e.g., elimination of regenerators for glass melters) and smaller flue-gas cleaning equipment. Despite significant progress in oxygen/natural gas combustor development, current technologies provide fairly low flame luminosity, which prevents them from achieving the full production rate and thermal efficiency increases that are possible with this process.
Because of this, GTI developed an oxygen/natural gas-fired burner that significantly increases production rate and thermal efficiency and reduces NOx emissions (even when using lower-cost industrial oxygen) compared with current oxygen/natural gas-fired technologies. GTI's high-luminosity burner (Fig. 2) increases thermal efficiency and decreases NOx formation by increasing radiative heat transfer to the load. This concept combines a fuel modification (preheating) zone with staged combustion.
A small portion (to 10%) of the natural gas is burned, and combustion products are mixed with the main source of natural gas, producing hydrocarbon soot precursors in a heated oxygen-free environment. Pre-heated natural gas then enters the first, fuel-rich, combustion zone and soot forms in the flame. The majority of the combustion occurs in the second (fuel-lean) combustion zone. Burning soot particles create a highly luminous flame that is more thermally efficient and cooler than a typical oxygen-gas flame. Heat transfer uniformity is increased and NOx emissions are significantly reduced.
The burner has been operating for more than a year on two glass furnaces (fiber and flat). It can be installed on new furnaces and can easily be retrofitted to existing air-gas and oxy-gas fired furnaces, including glass and metal melting, heating, material treating and cement clinkering. Sales on several glass furnaces are pending through GTI licensee, Eclipse Combustion Inc.
New York State Energy Research and Development Authority (www.nyserda.org) provided additional funding for this research.
Promising current programs
GTI is proud of the commercial successes that are the result of R&D performed in its Combustion Laboratory," says Abbasi. "As we look to the future, we're optimistic about our potential to provide impact through several novel programs that we're currently working on." Some of these programs are described on the following pages.
Partial-oxidation gas turbine (POGT)
In a project sponsored by CEC and GTI's gas industry programs, GTI teamed with Solar Turbines Inc. (http://esolar.cat.com) to develop a POGT for combined electricity generation, and hydrogen-enriched fuel-gas production for on-site industrial use.
When combined with a typical industrial system such as a high-temperature furnace or industrial boiler, the POGT offers end-users an overall system efficiency of at least 70-85%, with direct fuel-to-electricity conversion efficiency of 88%. Air emissions from the POGT are expected to be less than 3 ppm of NOx for electricity generation, with a 50-70% reduction for industrial boilers and furnaces. Significant reductions of carbon dioxide (CO2) emissions will result from improved efficiency and fuel utilization.
The POGT converts a portion of fossil-fuel energy to shaft energy, which, in turn, is used to generate electric power, as occurs within a conventional gas turbine. However, in the POGT, a high fuel-to-air ratio means that there is insufficient oxygen to combust all of the fuel, which results in a high-temperature, high-pressure, fuel-rich exhaust that can be efficiently used for other industrial processes.
The value of a POGT unit is realized when it is integrated at a selected industrial site according to Joseph Rabovitser, GTI's Director, Power Generation, Energy Utilization Center. Rabovitser says the industrial customer can generate power for on-site use or for sale at very high system efficiency, while the residual fuel improves environmental performance of on-site energy conversion units.
Supplemental FIR duct burner
Another combined heat and power (CHP) project by GTI and Coen Company Inc. involves the development of an innovative supplemental natural gas-fired burner to produce onsite heat and electricity. The burner (part of GTI's family of FIR burners) fires natural gas along with turbine exhaust gas to achieve maximum thermal efficiency, while at the same time reducing the amount of NOx emitted from a typical CHP system.
The use of a supplemental burner in a CHP system can increase thermal efficiency to more than 80%. However, current supplemental burners greatly increase NOx emissions. Specific objectives for this CHP system are:
- Reduce NOx to less than 20 vppm, corrected to 3% O2
- Achieve at least 35% NOx reduction compared with a gas turbine and conventional burner
- Provide ability to adjust the supplemental firing over a 3-to-1 ratio (turndown)
With this system, an FIR supplemental burner is installed at the exhaust duct of a gas turbine and uses turbine exhaust gas as a source of oxygen. This arrangement recovers thermal energy from the turbine exhaust for additional heat generation, which results in up to a 50% increase in thermal efficiency, and 12% higher efficiency than the microturbine and boiler operated separately.
Integrating a gas turbine with the FIR burner and a boiler allows the user to raise steam or hot water without increasing emissions. NOx created in the gas turbine is exposed to reducing conditions in a reburning zone of the FIR burner, resulting in overall NOx reduction compared with a power generator and boiler operating separately. Results of combustion-laboratory firing tests show the ability to increase efficiency and reduce NOx emissions simultaneously by more than 50%. Enbridge Consumers Gas and GTI's gas industry programs are funding the project.
Through its Super Boiler program, GTI is developing new, breakthrough steam-generation technologies. Successful development and commercialization of these Super Boiler technologies will potentially save U.S. industry over $10 billion annually in steam production costs and will minimize the environmental impact of steam generation throughout the U.S.
The objective of the program is to develop and demonstrate a first-generation Super Boiler (Fig. 3) by integrating novel technical concepts that can achieve efficiency levels above 94% and NOx emissions levels below 5 vppm on natural gas. As part of the project, GTI completed a technical review of the basic Super Boiler design parameters and teamed with Cleaver-Brooks (www.cleaver-brooks.com), a major U.S. packaged-boiler manufacturer.
GTI and Cleaver-Brooks integrated the combustion system, heat transfer elements and heat recovery system, combined with smart controls, into a compact firetube boiler, which is currently being laboratory tested. To date, the 3.6-million Btu/h (90 hp) laboratory boiler has met or exceeded all emissions goals up to full load, and the heat recovery system has reached 92% efficiency. The fully integrated Super Boiler system is scheduled to undergo field demonstration in 2005. DOE/ITP, Southern California Gas Co., Clever-Brooks and GTI's gas industry programs are funding the project.
Direct flame impingement (DFI)
Many industrial processes typically require rapid heat up of metals, which is currently accomplished using either gas-fired furnaces designed to use mainly radiative heat transfer or electric induction furnaces. GTI's DFI technology is aimed at producing a lower operating-cost option to traditional rapid heating techniques.
DFI technology increases convective heat transfer through special gas-fired burners, which produce high velocity jets of combustion gases directed at and subsequently flowing over and around a workpiece, such as a billet or a slab surface. It provides improved efficiency, fast startup, NOx levels below 50 vppm and a longer refractory life. GTI teamed with North American Manufacturing Company (www.namfg.com) to develop the technology. A section of a full-scale commercial prototype furnace is currently undergoing testing at GTI. The research is sponsored by DOE/ITP and GTI's gas industry programs.
Flexible-furnace test facility
GTI constructed a flexible-furnace test facility to evaluate a wide-range of industrial burners and combustion processes. The furnace (Fig. 4), designed and constructed by SECO/WARWICK (www.secowarwick.com) and GTI, will be used to evaluate the effects of furnace geometry (e.g., furnace shape, burner locations, exhaust locations, load locations) on thermal performance and emissions. It will also be used to evaluate convective and radiative heating, velocity patterns, the impact of burner operation on other burners, flame characteristics, heat release patterns and sensor measurements.
Researchers will be able to alter the interior shape of the furnace to match specific test needs. According to Dr. John Wagner, GTI's Principal Combustion Engineer, the facility will be unique among industrial test furnaces. It will be used for several current and future GTI projects, as well as to support collaborative industry research in combustion, energy efficiency and heat transfer.
Next-generation glass melter
TI is leading a consortium that includes six glass companies and several suppliers on a DOE/ITP project to deliver submerged combustion melting (SCM) to the glass melting industry. A next-generation melting system based on an oxy-gas-fired submerged combustion melter offers every performance characteristic that current melters offer plus decreased operating and capital costs, lower energy use and emissions, together with a simple design and high reliability. These new melters could be used immediately in applications requiring little glass refining, or integrated with future advancements in refining technology.
In SCM, an air-fuel or oxygen-fuel mixture is injected directly into a pool of hot melt. The combustion gases bubble through the bath, creating a high-heat transfer rate to the bath material and turbulent mixing. Melted material having a uniform product composition is drained from a tap near the bottom of the bath.
The new technique yields intense combustion, direct-contact, rapid heat transfer and rapid mass transfer (high thermal efficiency and reduced melter size). Additional funding is being provided by GTI's gas industry program. IH
Additional InformationAdditional related information may be found by searching these (and other) key words/terms via BNP Media LINX at www.industrialheating.com: nitrogen oxides, NOx, NOx emissions, flue-gas recirculation, combustibles, glass melters, glass refining, regenerators, flame luminosity, fuel-rich, fuel-lean, gas turbine, fossil-fuel energy, fuel-to-air ratio, steam generator, heat recovery system.
SIDEBAR: Collaboration possible for wide-ranging research
For years, GTI has looked at combustion research as an important component to maintain American manufacturing competitiveness. Through its Commercial/ Industrial Combustion Laboratory, GTI continues to develop solutions and deliver results to this important market.
GTI's Combustion Laboratory houses the following equipment:
- Seven research furnaces ranging from 100,000 to 5 MMBtu/h, which allow simulation of a wide range of industrial process heating equipment. High temperature furnaces (100,000, 500,000, 3 MM and 5 MMBtu/h) with variable loads can simulate almost any industrial process heating environment. These include: (1) A 1 MMBtu/h integral quench radiant tube heat treating furnace, (2) A 1 MMBtu/h indirect-fired flat radiant panel furnace, (3) A 1.2 MMBtu/h furnace to study and develop heating concepts that maximize convective heat transfer rates
- Two boiler/process heater simulators (5 and 12 MMBtu/h)
- A 20 MMBtu/h packaged watertube test boiler, which can be used to test a single burner, or to study flame interactions between multiple burners
- A 3 MMBtu/h submerged combustion melter
- An automated infrared-heater testing platform
- A bench-scale facility to study flame characteristics and develop new combustion, sensors and controls concepts
- An extensive array of emissions and performance measurement and data acquisition systems
For information on collaborating with GTI on combustion research programs, contact Hamid Abbasi, GTI's Executive Director, Energy Utilization Center; tel: 847-768-0585; e-mail: firstname.lastname@example.org; Web: www.gastechnology.org.