Industrial Applications

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Participant
Coal Tech Corporation

Location
Williamsport, Lycoming County, PA (Tampella Power Corporation's boiler manufacturing plant)

Plant Capacity/Production
23 x 10⁶ Btu/hr of steam

Coal
Pennsylvania bituminous, 1.0-3.3% sulfur

Technology
Coal Tech's advanced, air-cooled, slagging combustor

Additional Team Members
Commonwealth of Pennsylvania, Energy Development Authority
cofunder
Pennsylvania Power and Light Company
supplier of test coals
Tampella Power Corporation
host

Project Funding

Project Objective
To demonstrate that an advanced cyclone combustor can be retrofitted to an industrial boiler and that it can simultaneously

remove up to 90% of the SO₂ and 90-95% of the ash within the combustor and reduce NOx to 100 ppm.

Technology/Project Description
Coal Tech's horizontal cyclone combustor is lined with an air-cooled ceramic. Pulverized coal, air, and sorbent are injected tangentially toward the wall through tubes in the annular region of the combustor to cause cyclonic action. In this manner, coal-particle combustion takes place in a swirling flame in a region favorable to particle retention in the combustor. Secondary air is used to adjust the overall combustor stoichiometry. Tertiary air is injected at the combustor/boiler interface. The ceramic liner is cooled by the secondary air and maintained at a temperature high enough to keep the slag in a liquid, free-flowing state. The secondary air is preheated by the combustor walls to attain efficient combustion of the coal particles in the fuel-rich combustor. Fine coal pulverization allows combustion of most of the coal particles near the cyclone wall. The combustor was designed so that a high percentage of the ash and sorbent fed to the combustor is retained as slag. For NOx control, the combustor is operated fuel rich, with final combustion taking place in the boiler furnace to which the combustor is attached. The SO₂ is captured by injection of limestone into the combustor. The cyclonic action inside the combustor forces the coal ash and sorbent to the walls where it can be collected as liquid slag. Under optimal operating conditions, the slag contains a significant fraction of vitrified coal sulfur. Downstream sorbent injection into the boiler provides additional sulfur removal capacity.

In Coal Tech's demonstration, an advanced, air-cooled, cyclone coal combustor was retrofitted to a 23 x 10⁶ Btu/hr, oil-fired package boiler located at the Tampella Power Corporation boiler factory in Williamsport, Pennsylvania.

Coal Tech Advanced Cyclone Combustor Process Flow Diagram
Larger jpeg or wmf version

Results Summary

Environmental

• SO₂ removal efficiencies of over 80% were achieved with sorbent injection in the furnace at various calcium-to-sulfur (Ca/S) molar ratios.

• SO₂ removal efficiencies up to 58% were achieved with sorbent injection in the combustor at a Ca/S molar ratio of 2.0.

• A maximum of one-third of the coal's sulfur was retained in the dry ash removed from the combustor (as slag) and furnace hearth.

• At most, 11% of the coal's sulfur was retained in the slag rejected through the combustor's slag tap.

• NOx emissions were reduced to 184 ppm by the combustor and furnace, and to 160 ppm with the addition of a wet particulate scrubber.

• Combustor slag was essentially inert.

• Ash/sorbent retention in the combustor as slag averaged 72% and ranged from 55 - 90%. Under more fuel lean conditions, retention averaged 80%.

• Meeting local particulate emissions standards required the addition of a wet venturi scrubber.

Operational

• Combustion efficiencies of over 99% were achieved.

• A 3-to-1 combustor turndown capability was demonstrated. Protection of combustor refractory with slag was shown to be possible.

• A computer-controlled system for automatic combustor operation was developed and demonstrated.

Economic

• Because the technology failed to meet commercialization criteria, economics were not developed during the demonstration. However, subsequent efforts indicate that the incremental capital cost for installing the coal combustor in lieu of oil or gas systems is $100-200/kW.

Project Summary
The novel features of Coal Tech's patented ceramic-lined, slagging cyclone combustor included its air-cooled walls and environmental control of NOx, SO₂, and solid waste emissions. Air cooling took place in a very compact combustor, which could be retrofitted to a wide range of industrial and utility boiler designs without disturbing the boiler's water-steam circuit. In this technology, NOx reduction was achieved by staged combustion, and SO₂ was captured by injection of limestone into the combustor and/or boiler. Critical to combustor performance was removal of ash as slag, which would otherwise erode boiler tubes. This was particularly important in oil furnace retrofits where tube spacing is tight (made possible by the low-ash content of oil-based fuels).

The test effort consisted of 800 hours of operation, including five individual tests, each of four days duration. An additional 100 hours of testing was performed as part of a separate ash vitrification test. Test results obtained during operation of the combustor indicated that Coal Tech attained most of the objectives contained in the cooperative agreement. About eight different Pennsylvania bituminous coals with sulfur contents ranging from 1.0 - 3.3% and volatile matter contents ranging from 19 -37% were tested.

   The Coal Tech combustor.

Environmental Performance
A maximum of over 80% SO₂ reduction measured at the boiler outlet stack was achieved using sorbent injection in the furnace at various Ca/S molar ratios. A maximum SO₂ reduction of 58% was measured at the stack with limestone injection into the combustor at a Ca/S molar ratio of 2. A maximum of one-third of the coal's sulfur was retained in the dry ash removed from the combustor and furnace hearths, and as much as 11% of the coal's sulfur was retained in the slag rejected through the slag tap. Additional sulfur retention in the slag is possible by increasing the slag flow rate and further improving fuel-rich combustion and sorbent-gas mixing.

With fuel-rich operation of the combustor, a three-fourths reduction in measured boiler outlet stack NOx was obtained, corresponding to 184 ppm . An additional reduction was obtained by the action of the wet particulate scrubber, resulting in atmospheric NOx emissions as low as 160 ppm.

All the slag removed from the combustor produced trace metal leachates well below EPA's Drinking Water Standard.

Total ash/sorbent retention as slag in the combustor, under efficient combustion operating conditions, averaged 72% and ranged from 55 - 90%. Under more fuel-lean conditions, the slag retention averaged 80%. After the CCT project, tests on flyash vitrification in the combustor, modifications to the solids injection system, and increases in the slag flow rate produced substantial increases in the slag retention rate. To meet local stack particulate emission standards, a wet venturi particulate scrubber was installed at the boiler outlet.

Operational Performance
Combustion efficiencies exceeded 99% after proper operating procedures were achieved. Combustor turndown to 6 x 10⁶ Btu/hr from a peak of 19 x 10⁶ Btu/hr (or a 3-to-1 turndown) was achieved. The maximum heat input during the tests was around 20 x 10⁶ Btu/hr, even though the combustor was designed for 30 x 10⁶ Btu/hr and the boiler was thermally rated at around 25 x 10⁶ Btu/hr. This situation resulted from facility limits on water availability for the boiler. In fact, due to the lack of sufficient water cooling, even 20 x 10⁶ Btu/hr was borderline, so that most of the testing was conducted at lower rates.

Different sections of the combustor had different materials requirements . Suitable materials for each section were identified. Also, the test effort showed that operational procedures were closely coupled with materials durability. As an example, by implementing certain procedures, such as changing the combustor wall temperature, it was possible to replenish the combustor refractory wall thickness with slag produced during combustion rather than by adding ceramic to the combustor walls.

The combustor's total operating time during the life of the CCT project was about 900 hours. This included approximately 100 hours of operation in two other flyash vitrification test projects. Of the total time, about one-third was with coal; about 125 tons of coal were consumed.

Developing proper combustor operating procedures was also a project objective. Not only were procedures for operating an air-cooled combustor developed, but the entire operating data base was incorporated into a computer-controlled system for automatic combustor operation.

Commercial Applications
The goal of this project was to validate the performance of the air-cooled combustor at a commercial scale. While the combustor was not yet fully ready for sale with commercial guarantees, it was believed to have commercial potential. Subsequent work was undertaken, which has brought the technology close to commercial introduction.

Contacts

Bert Zauderer, President
  Coal Tech Corporation
  P. O. Box 154
  Merion Station, PA 19066
  (610) 667-0442
  (610) 667-0576 (fax)
  bz.coaltech@verizon.net

William E. Fernald, DOE/HQ, (301) 903-9448
  william.fernald@hq.doe.gov

Thomas A. Sarkus, (412) 386-5981
  sarkus@netl.doe.gov

Web Site:
 www.coaltech.biz