COAL SLU RRI ES: 26637 ‘’IC

AN ENVIRONMENTAL tion plant and pipelines, at &in Huang Dao. China has also com- BONUS? mercialized a handful of smaller

evelopers and promoters of coal-water slurries and simi- lar CWF (coal-water fuel) D technologies have had a hard -

time winning converts since they un- veiled their first commercial processes in the 1970s. The economic appeal of such processes, marginal at best (box, p. 37), varies with the price of oil - now at its lowest level since late 1988, according to the U.S. Energy Information Admin- is tration (Washington, D . C . ) .

Nevertheless, the technology is per- colating, as geopolitics and environ- mental pressures drive new processes. Such fuels are becoming increasingly important to coal-rich, oil-poor nations such as China, as they attempt to build an onshore fuel supply. Meanwhile, im- provements are changing the way coal- fired processes are viewed. Where air pollution regulations once discouraged the use of coal fuels, new coal processes have been developed that cut nitrous oxides (NOx) emissions (CE, January, p. 28) and provide a use for coal fines, previously viewed as waste.

The latest developments in the field were all on display at the 19th Interna- tional Technical Conference on Coal Utilization and Fuel Systems, held in Clearwater, Fla., on March 21-24. At this annual meeting, sponsored by the Coal & Slurry Technology Association. (Washington, D.C.) and the Pittsburgh Energy Technology Center of the U.S. Dept. of Energy (PETC),* some 200 vis- itors from around the world gathered to discuss the latest developments in coal slurry utilization - new and im- proved processes, and onstream plants. * Copies of the meeting’s proceedings are avail- able from Coal&Slurry Technology Assn , 1156 15th St NW, Suite 525, Washington, DC 20005; Telephone (202) 296-1133

34 CHEMICAL ENGINEERING/MAY 1994

Only marginally economical,

coal slurry fuels may help solve

some air pollution and land disposal

problems The latest developments span the

globe. In Porto Torres, Sardinia, Enichem S.p.A. (Milan) started up the first phase of an integrated coal benefi- ciation and combustion system last summer. Its 500,000-m.t./yr plant uses Snamprogetti S.p.A.’s (Milan) Reocarb process, and coal from Venezuela and Colombia.

In China’s Shandong province, in Rizhao, Yanri CWM Co., a consortium of Japanese and Chinese firms, has built a 250,000-m.t./yr coal slurry pro- cessing plant. Part of its output is shipped to Kyushu, Japan (route shown above), for use at power plants and industrial boilers. Meanwhile, on- shore in Japan, COM Co. is producing 650,000 m.tJyr of a coal-oil mixture that is burned at Tokyo Electric’s Yokosuka power station.

Currently, Chinese mine operators and government officials are seeking to develop a project, including a produc-

plants, some using waste coal fines, that provide fuel to nearby industrial boilers or furnaces.

In the Commonwealth of Indepen- dent States (CIS), Snamprogetti has completed work on a huge system in Siberia - 3 million m.t./yr - to trans- port slurry between Belovo coal mines and a 1,320-MWe power complex in Novosibirsk. Designed to optionally beneficiate the coal, transport it at 500 m3/h, and burn it in six 220-MWe units, the project has, so far, run only inter- mittently since it was completed in 1992.

In the U.S., a number of small demonstration projects or tests have been conducted in recent years to add to the data already accumulated since the late 1970s; most of these projects are supervised by the U.S. Dept. of En- ergy (DOE; Washington, D.C.). The big U.S. news from the March meeting, however, was a project at Pennsylvania Electric Co.’s (Penelec, Johnstown, Pa.) Seward plant, near Homer City, Pa. Penelec has tested a system where a slurry of waste coal fines, a byproduct of beneficiation, was used to supple- ment conventional pulverized-coal combustion in a 32-MWe boiler.

A mountain of coal fines The Penelec project garnered the most excitement of U.S.-based slurry propo- nents because it has a good chance of proving economically viable. Currently, over half of all US. coal is coarse- ground and washed to remove pyritic sulfur and to reduce ash content.

“Fines produced during this benefici-

+ ,’ 2

” NEWSFRONT

ation make transporting, storing and using the coal much more difficult, so utilities require their removal,” notes Todd Sommer, vice-president for engi- neering services at Energy and Envi- ronmental Research Corp. (EER, Irvine, Calif.). For years, the fines have been disposed along with ash and other reject material in huge impoundments at the mine mouth or adjacent to bene- ficiation plants. “Even so, it is rela- tively easy to separate them from ash, by flotation processes,” notes Sommer.

At least 10% of the organic content of coal processed today is lost to fines, and an estimated 2-5 billion tons of fines are buried in impoundments around the U.S. While no regulations have been issued restricting the current fine disposal practice, many in the utility industry can see a day when impound- menta must be cleaned up as an envi- ronmental hazard - and they want to be ready.

The Penelec demonstration began in September, after the utility readied a CWF pilot plant at its Homer City, Pa., beneficiation plant. EER modified the pulverized-coal boiler to accept CWF that is air-atomized in the burners. CWF co-firing with pulverized coal was supposed to be gradually stepped up to

40% of the Btu input of the boiler, but the startup went so smoothly the oper- ators immediately went to the full test, according to Joseph Battista, project manager at Penelec.

Over a dozen test runs have been completed with slurries whose coal con- tent ranges between 26 and 48%, with- out additives. Problems are now being worked on: The slurry, for example, can settle out, resulting in the lower-than- targeted 48% coal content. The CWF pilot plant also has much less capacity than would be necessary for continuous operation; Penelec plans to run 24-h tests now, and eventually to work with a commercial-volume supplier of CWF.

Ideal additives Japan, arguably the most advanced na- tion currently in CWF technology, has been spurred by a desire to diversify its energy sources away from oil. As such, its industry efforts are focused on high- coal-content (70%) fuel, with additives that maintain slurry uniformity.

“The cost of CWF can generally be di- vided in two - half for the coal itself and half for processing,” observes Tat- suo Nakanishi, manager of the Techni- cal Development Dept. of the Center for Coal Utilization, a Tokyo research of-

fice. “Of the processing cost, additives account for 20% Le., 10% overall].” Several industry and academic projects have been under way to develop appro- priate additives, including car- boxymethylcellulose, polymethacrylate and polystyrene sulfonic acid; biopoly- mers such as xanthan gum, and a pro- prietary formulation called s-130 and S-194 from Dainihon Seiyaku Co. (Tokyo).

“It is impossible to say which addi- tive is best,” says Hiromoto Usui, a chemical engineering professor at Ya- maguchi University. “It depends on what type of coal is being used, and how the coal is to be processed.” He adds that the search is continuing to find lower-cost additives, but that this is an “elusive” goal. Lion Corp. (Tokyo) has worked closely with Japan COM Co., and the two have settled on the sulfonic acid derivative as having the best combination of stabilization and low viscosity buildup in the mixture.

Standing behind most of the Japan- ese CWF efforts is JGC Corp. (Tokyo), which is an investor in Japan COM and the Yanri CWM project in China. It also owns the rights to the Carbogel CWF process, originally developed by AB Carbogel (Helsingborg), a Swedish company that JGC bought in 1992.

In Europe, Snamprogetti is the dom- inant player. The company has devel- oped a coal beneficiation process, a CWF process, and has worked on pipeline technology for shipping CWF. The just-opened Porto Torres project was carried out with the support of EN1 (the National Energy Agency of Italy) and the Italian government. According

COAL AND W m ? A PERFECT MIX?

oal slurries have been touted for C at least 20 years as a way of tum- ing a solid fuel into an wily trans- ported, easily cleaned and easily bum& “liquid“ fuel, without the lnten- sive energy consumption necessaty to actually produce liquefied coal fuels. Earty work in the 19709 established the technology’s value as a transporta- tion technique, and the Bkck Mesa pipeline in the United stales (between a Peabody Coal Co. mine in northeast- em Arizona and the Mohave Generat- ing station in Laughlin, Nev.) has been running successfully since 1970. This coal slurry, however, is distinguished from coal-water fuel (CWF) because it is not ground so fine, according to Henry Brolick, president of Black Mesa Pipeline, Inc. (Tulsa, Okla). Typically, the slurry has a 50% water

content, and the coal is ground to par- ticles around i mm. Coal-water fuel, in contrast, usually has a 3040% water content, and the coal is ground to 100 pm. High-coal-content fuel requires the use of surfactantdispersant addi- tives to keep the coal partides in sus- pension. While these are only 1-2% of the fuel, they can add 10% or more to its cost. Fuel prices vary widely around the

world; in the US. , recent economic evaluations have put the cost of CWF at, or some 10-1 5% below, the cost of ctmventional pulverized coal fuel. That margin is not enough to attract the in- tmst of u t i l i operators who must cOnsider the added or modified equip- ment to bum CWF. Cost is the factor that has hobbled

another form of coal slurry, the coal-oil mixture (COrJr). Although a number of demonstrations were conducted in the U.S. and Europe a decade ago, the only ongoing project using COM is Japan COM Co’s Onahama plant. Utilities have a number of options

when considering CWF. Bumers de- signed to run on oil have been suc- cessfully converted to CWF; a 10% or so =derating” occurs because the Btu content of the fuel is less than that of oil. CWF can also be used to supple- ment or replace existing pulven’zed- coal bumers, the most common type of burner used by US. utilities today. However, oil-buming furnaces must be modified to account for the buildup of ash on boiler tubes, on the fumace floor, and in air-emission controls. Re- ducing ash content by beneficiating coal is one solution. Sulfur that is not locked into the organic portion of the coal can also be reduced, lowering the burden on SOX scrubbers. 0

Penn State University

2.000

I Stack

ilse ibt

Ash removal - system L

Heat pipe heat exchanaer

This pilot scale unit, which is now running Natural gas

and generating heat f& steam Pennsylvania State University,

shows the basic elements of any coal water fuel utilization plant

Strainer

3ARBARA BERASI

to a presentation at the Cleanvater meeting by Dario Ercolani, a project manager a t Snamprogetti’s Fano, Italy, R&Dcenter, the plant is designed to beneficiate Colombian coal with an ash content of 12% and 0.9% sulfur to 3.5% ash and 0.5% S. The plant has already run tests using Venezuelan coal with- out beneficiation that has been slurried with Snamprogetti’s Reocarb process. The company designed and built a mi- cronizing ball mill and a finishing rod mill for a “bimodal” process that mini- mizes the loss of coal fines while maxi- mizing ash and sulfur removal.

The greening of coal As these international projects get off the ground, CWF proponents are start- ing a new round of research efforts fo- cusing on the fuel’s environmental ben- efits. Compared with conventional pulverized coal combustion, the fuels can cut NOx emissions by as much as 40%, since the presence of water in the burners lowers flame temperatures and maintains a fuel-rich atmosphere, according to Kelly Thambimuthu, a re- searcher with the International Energy Agency Coal Research Group (London).

In the future, he says, CWF could also be mated with pressurized flu- idized bed combustors, a new genera- tion of furnaces for burning coal with lower SOX emissions. Because these units run at around 220 psig, pulver- ized coal must be made into a paste with water before being injected; CWF

already exists in a slurry with water. EER also hopes to commercialize a

low-NOx “reburn” technique, in which CWF is injected above the radiant- heating zone of a boiler combusting pulverized coal. The secondary fuel in- jection creates a reducing environment where NOx compounds formed at the primary burners are reacted to nitro- gen. Reburning, or staged combustion, is a technique for controlling NQx that it is usually considered for natural gas, but EERs Sommer says that using it with CWF could be much cheaper. EER has tested the process and is looking for a utility demonstration.

Japan COM plans to expand its process range by developing a lignite- based CWF, which would be less expen- sive than CWF using high-rank bitumi- nous coals. A 350-kgh plant opened this spring using the process, and tests should run through 1996, sponsored by the Ministry of International Trade and Industry (MITI; Tokyo).

Proponents of CWF say that its use is inevitable, no matter how low oil prices fall, simplybecause thereis somuchcoal in the world, and oil’s availability and price are so uncertain. We are trying to keep this technology alive, because in the future it will be economical,’’ con- cludes John Window, program coordi- nator for DOE’S Coal Utilization Div. Should oil prices climb, C W is ready to

Nicholas Basta, with Stephen Moore and Gerald Ondrey

step in - if consumers need it.

CHEMICAL ENGlNEERlNGlMAY 1994 37