Process steam is the life-blood of food and beverage processing plants. Without the vital heat energy contained in steam,today's quality beers could not be brewed. Breweries have always derived this essential processing element from the traditional fossil fuel sources of coal, oil and natural gas.
Unfortunately, the rising trend in the cost of fossil fuels continues, and the time is approaching when prudent brewery management must plan for the era when other energy sources and their associated combustion methods, innovative as they may now seem, will demand investigation and implementation.
Energy Alternatives
For breweries, possible alternate energy sources must be considered on the basis of their potential application for steam generation. This paper will touch on the various alternate energy possibilities, including solar energy, geothermal energy, wind energy, atomic energy, and the replenishable organic energy available from forest products.
Solar Energy
Either directly or indirectly, the sun has furnished through radiation of heat and light all of the energy which supports life on earth. All food and fuels in the final analysis are derived from vegetation that has utilized the energy of sunlight.
At the sun's surface, radiant energy is developed at a rate in excess of 37 k.w. per square inch. After traveling the 93 million miles to earth, the total energy developed has decreased to about 1.12 kw. per square yard.
Yet, no truly efficient collection and retrieval system for solar energy has yet been developed. Most of the research thrust has been focused on direct conversion of sunlight to electrical energy, the resultant power being usable primarily in limited demand operations.
A case in point is the crop irrigation system built by the Energy Research and Development Administration for an experimental farm near Mead, Nebr., which is designed around a solar collector containing 120,000 solar cells. At peak sunlight, the cells generate nearly 25 kw. and, combined with battery storage, provide the power to operate one 10 h.p. pump. At a cost of $15.50 per watt, the price to duplicate this installation would be prohibitive.
More applicable to process steam generation would be the solar furnace, the first of which was built at Jena. Germany, in 1921. At present the world's largest solar furnace has been constructed by the French government in the Pyrenees mountains at Odeillo. It consists of over 20,000 mirrors mounted in a gigantic parabolic wall which concentrates the sun's rays onto a target. Temperatures of nearly 4,000' F have been achieved, more than adequate for steam generation - barring periods of darkness, or even cloudiness.
Geothermal Energy
Geothermal energy is limited to certain areas of the United States where magma-related activity produces high temperatures near the earth's surface. Two methods to harness this energy are used. One depends on the utilization of near surface boiling water which is made available for heating. The other involves drilling into an.active area to tap an underground source of high pressure steam and vapor. It is the second approach that is taken by most geothermal power generating stations typical of which is an American-built unit at Geysers, Calif., which produces 500 megawatts. The obvious drawback to universal geothermal steam production is its dependency on a favorable location.
Wind Power
Catching the wind and converting its energy into useful work has been successfully accomplished by many cultures. Windmills in Holland have been in operation for several centuries and are still being used. In the rural areas of the United States, windmills by the thousands tower over farms and ranches, pumping water and generating small amounts of electrical power.
Only in the recent past has research effort been applied in the field of air-foil design efficiencies. This work has generated a family of sophisticated air-foil shapes which take maximum advantage the power inherent in the earth's air current flow. At the Sandia Laboratory in Albuquerque, N.M., a seven-story high, vertical axis wind turbine is presently undergoing testing. The turbine has been projected to develop 60 kw in a 28 m.p.h. wind. Again, this approach, while producing a limited amount of electrical power, is still not suitable for steam production, and, like geothermal power, is restricted to given areas of suitability.
NucIear Energy
The production of steam through use of nuclear energy utilizes the fission process whereby the nucleus of a heavy atom is split into two lighter atomic nuclei, releasing in the process a substantial amount of energy. In this process, neutrons are also released to split other atoms and thereby produce a controllable chain reaction. This controlled chain reaction produces a continuous supply of heat which can be used to make steam.
Some idea of the energy released by the fissioning of Uranium-235 can be gained from the fact that one gram of U-235 fissioned is equivalent to approximately 24,000 kilowatt hours or 81.9 x 10^6 BTU's. While nuclear energy is admirably suited to the low cost production of steam for electric power generation, it is questionable whether the state of the art will be advanced to the point where nuclear-based process steam use will be allowed in the food industry or, if allowed, accepted by consumers.
Replenishable Organic Energy (ROE)
The most attractive of all the alternate energy sources appears to be utilization of the replenishable organic energy available from forest materials. There are millions of tons and millions of acres of forest materials in the United States alone, and anyone who has flown over the vast areas of the great American forest can appreciate the magnitude of translatable energy contained in this gigantic biomass; It is this biomass source of energy, undergoing constant replenishment, that is to be examined from the standpoint of practical implementation.
ROE Defined
ROE can be described as the biomass energy contained in the various kinds of trees, such as hardwood, softwood, popple, etc., that make up the nation's forest material resource. It also includes all of the by-products and mill residues from wood processors, along with bark, wood chips, and rough or unusable trees of commercial and other species.
The general statement can be made that the energy content in a ton of green wood (50 percent moisture content) is equal to the energy contained in 8,800 cubic feet of natural gas, 704 lbs. of coal, or 1.4 barrels of oil. It can be assumed that a pound of bone-dry ROE will contain about 8,800 btu.
ROE Quantity
Every year, 120 million tons of bone-dry wood and bark from harvesting operations alone are simply discarded. This amount is equivalent to about 84.5 million tons of coal. Additionally, the volume of non-commercial timber in the eastern United States alone, including rough and rotten trees plus salvageable dead trees, is estimated by the Forest Service at about 10^9 tons bone dry, equal to 7 x 10^8 tons of coal.
In the state of Michigan alone, 20 per cent of the commercial forest is unmarketable wood that takes up growing space. This cull wood represents about 52 million tons of wood at about 4400 but/lb which 72.6 x 10^6 barrels of oil.
The northeastern part of the United States has about 32 million acres of dense hardwoods, and in the south, the southern pine hardwood forests comprise over 100 million acres, a total of over 132 million acres for the two areas.
These hardwood forests can be thinned out profitably to allow more growing space for manufacturable wood. A mechanized thinning operation in Michigan by the U.S. Forest Service provided a yield of 50 tons of green wood per acre. Thus, the cull wood energy potential alone in the northeastern and southern hardwood areas is equivalent to about 9.2 x l0^9 barrels of oil.
MiII and Manufacturing Residues
A typical hardwood mill will produce about 1.69 tons of wood residue per 1,000 board feet of marketable wood. It has been estimated that mill residue production for the nation as a whole is on the order of 110 x 10^6 tons annually.
Manufacturing residues consist mainly of seasoned chips, trimmings, and sawdust with a much lower moisture content than green forest cuttings. This residue represents a substantial daily production and lends itself well for use as fuel.
An insight into the daily national production of manufacturing residue can ~be gained by noting that a single furniture manufacturing company in Leinore, N.C., has a residue output of 300 tons of ROE per day. This residue, with a moisture content of 22 per cent, has an equivalent to No. 6 fuel oil as follows:
300 tons x 2,000 lbs. = 600,000 lbs/day x 78 per cent = 468,000 lbs. of bone dry ROE
468,000 lbs. x 8,800 btu/lb = 4.12 x 10^9 btu / 150,150 btu/gal oil = 27,429 gal.
27,429 gal. / 42 gal/bbl = 653 bbl. of #6 fuel oil.
Multiplying this total by the hundreds of wood product manufacturers in the nation indicates a significant fuel oil equivalent in terms of energy that is being generated daily, much of it going to waste.
Firing Systems
Saw mills and paper mills have for many years fired ROE residue to provide heat and steam, using spreader stokers that utilize wood and bark chips in a manner to the burning of coal. Some companies have found it economically advantageous to burn a combination of the two fuels, which in many instances lowered the sulfur content in the stack output.
In most cases, heating efficiencies vary inversely with the moisture content of the fuel. The firing cycle demands that the moisture in the fuel must first be evaporated. After evaporation, the combustible gases burn, leaving the carbon fraction. Combustion of the final carbon fraction results in the maximum heat release.
Corner Tube Boiler (CTB)
The search for ROE firing methods has popularized the use of the corner tube boiler. This boiler type, developed in Germany about 30 years ago, is now used mainly for burning municipal waste and refuse. Over 150 units are in use worldwide, with the largest installed at Saugus, MA which consumes 750 tons per day. Each of the Saugus units can generate 160,000 to 200,000 lb./hr. of steam at 690 psig and 87 degrees F. The CTB could burn ROE based fuels without difficulty.
Wood Chip Boiler
An example of the advantages of converting to ROE fuel is the approach taken by the Russell Corp. of Gatlinburg, Tenn. In January, 1976, the company in stalled a wood-chip boiler with a capacity of 120,000 lb/hr of steam, firing nearly 500 tons of wood chips per day. Initially, the boiler cost was $1.7 million, and adding economizers and wet scrubbers brought the total cost to $2.3 million. E. C. Gwaltney, the president of the firm, estimates savings of about 18,000 gallons of fuel oil per day. He also said that, based on the availability of wood chips, and the price of fuel oil, payout on the installation would be achieved in less than five years.
Pelletized ROE Firing
There are a number of energy companies today who furnish equipment to fire ROE in its many available forms. One such organization is the Guaranty Performance Co. of Independence, Kansas., which has evolved a unique system to take advantage of the ROE generated from the fabrication of wood products.
The firm produces solid fuel pellets from wood wastes by drying these byproducts in a rotary dryer of their own design. The dried ROE is converted to a desired size and subsequently pelletized into a cylindrical shape approximately one-fourth inch in diameter by three-eighths inches long. A portion of the fuel pellets produced is used to fire the dryer and the remainder is available for sale to energy users under the "ROEMMC" trade name.
The ROEMMC fuel is guaranteed by the company to contain a minimum of 8,000 ROE/lb., although the actual ROE content usually far surpasses this figure. The fuel is burned most efficiently in the company's furnace designed especially for the fuel, although the pellets could easily be burned along with coal in a pulverized coal boiler. In areas where there are forest products companies, user cost for the ROEMMC fuel could be as low as $1.25 per million btu's, about the same price or less as 12,500 btu coal.
Guaranty Performance Co. has installed a ROEMMC burner system at the Bassett Furniture Co., Bassett, Va., which is used to fire a 25,000 lb./hr. Keeler boiler. There is also a ROEMMC system installed and running at the Union Camp Pulp and Paper Co. in Franklin, Va. At present, the largest ROEMMC burner has a heat release of 60 million btu/hr, easily attains a steam generating rate of 50,000 lb./hr.
Summary
Of the approaches to alternative energy sources considered, it would appear that for process steam generation, replenishable organic energy ROE, is economically the most attractive. This energy supply has an estimated availability potential of 400 to 500 million tons per year, and with rigorous national forest management program, the available amount of this tremendous form of biomass energy could rise to a quantity approaching one billion tons per year without ever reducing commercial forest acreage. It would be both economically and environmentally sound.
Article revised by author since original publication
Email Address: drer@execpc.com
Back to The Richards Engineering Group, Ltd.