The Feasibility of Converting Waste to Energy: An Analysis
by Melvin Fiegi

ABSTRACT

The feasibility of this process is based on research, interviews and actual experience with developing new products and processes.

The analysis of this process and comparing it to any present processes shows that converting waste to energy is possible and practical. This report addresses different problems and solutions for those problems by using this technology. The analysis shows great potential as a new business while improving our environment at the same time.

Converting waste to energy is the best possible solution to deal with the scrap tire problem. It is a very viable process for reducing the size of our landfills. This process would solve garbage problems that exist on islands like Hawaii. By converting the system to hydrogen fuel, air emission pollution can be reduced further.

Anyone interested in investing in a business of the future should definitely look at this process and all its advantages.

• Since stockpiles of scrapped tires are growing, and landfills need to be reduced, converting tires to energy is the most practical solution.
• Fluidized combustion is the best solution to reducing the volume of garbage and also reducing air pollution released from combustion of garbage.
• The process of combustion described will generate electricity, reduce CO2 emissions, and reduce the stockpiles of scrap tires without creating pollution.

Introduction

This paper describes a garbage-burning system that minimizes carbon dioxide (CO2) and eliminates air pollutants. Our direct-fired fluidized bed can burn any combustible material efficiently. Of course, not all materials put into the garbage are combustible. We have developed systems to sort out these materials and recycle them or dispose of items that can't be recycled. Fluorescent bulbs, batteries, rechargeable flashlights, computer components, and many other materials are considered hazardous and shouldn't be put in the garbage.

We are able to convert scrap tires into energy and accomplish it without pollution. We will not grind them up but burn them as a complete unit. There are 280 million used tires that need to be disposed of every year in the U.S. The energy from one combusted tire is equivalent to 3 gallons of oil, so 280 million burned scrapped tires equal 840 million gallons of oil ("Tire"). Environmental Protection Agency (EPA) estimates two to three billion scrapped tires are stockpiled in the United States ("Air"). The most common method of disposing of tires is accomplished by grinding them up and then processing them. This is like pumping water uphill and letting it run back downhill to generate electricity. It takes more energy to get it to the top of the hill than energy generated going downhill. Also, the need to dispose of computer parts is huge, but first these components need to be broken down into materials that can be recycled and materials that can be converted into energy. The National Recycling Coalition estimates that by 2007 there will be 500 million obsolete computers. It is estimated that in the U.S. 700,000 computers become obsolete every year with only 10% of the material being recycled (Goodrich). We have a plan to resolve these problems which will be discussed later.

We can take 2000 pounds of material that would be going into landfills, and by burning it, reduce it down to 300 pounds of ash. The EPA estimates that one ton of garbage would generate 525 kilowatt-hours (kWh) of electricity. When waste is burned at temperatures over 2000 degrees Fahrenheit, most chemicals are broken down into simpler, less harmful compounds. At this time in the U.S. we only burn 16 percent of our trash in waste-to-energy plants. Many of these plants can be modified with our pollutant-reducing methods to reduce air pollution and CO2 emissions ("Waste").

Hazardous Waste Combustion

The EPA states that one of their larger problems is with burning hazardous waste. There are 172 facilities burning 3.3 million tons of hazardous waste in the United States every year. The following pollutants are being discharged from these plants every day: dioxin, furan, lead, mercury, hydrochloric acid, and metals ("Environmental"). Unfortunately, most of these plants use industrial boiler types of furnaces to burn hazardous materials. This type of facility doesn't burn material at a high enough temperature to control pollutants coming out of their stacks. In Oregon, we release 201 million pounds of toxic pollutants per year; we recycle 66 million pounds of these toxic pollutants. This means that we have 135 million pounds a year left to dispose of. We are ranked 31st in the nation, so it's easy to see how big the problem really is ("Oregon"). Remember this is toxic material only, not the total garbage we dump every year.

Garbage Burner

The method of burning garbage we are using is a direct-fired fluidized bed chamber
(Figure 1). A direct-fired fluidized bed is best explained as a bed of sand that has an air/natural gas mixture bubbled up through it which makes the sand float or flow.

Figure 1. Fluidized bed combustion chamber
Source: Foundry

We plan to introduce sand and garbage from the top and provide full fluidization wall-to-wall in the burning chamber. The air and gas supplied to the burner part of the system are automatically introduced through a special distribution system. This is controlled by a Programmable Logic Control (PLC) to maintain a constant temperature and an even rate of fluidization. We will maintain a temperature between 2800 and 3200 degrees Fahrenheit. Costs are reduced because the garbage we are introducing to the chamber is combustible; therefore, the amount of natural gas used to maintain a constant temperature is reduced. The burning chamber is made of heat-resistant steel, and ceramic fiber is used as insulation. Because we don't use the more costly refractory linings (high temperature insulation), the preheat time is reduced from hours to minutes. Sand and garbage flow is easily regulated through the burner to insure complete combustion and even fluidization. Since the materials being burned are fluidized, it isn't possible for materials to collect in clumps and not burn. The sand and ash flow out of the burn chamber on the opposite side, at a set height. Once the ash and sand are discharged, they are separated. The sand is reused, and the ash is recycled into other products. The fly ash (lighter airborne ash) that goes out the upper part of the burn chamber is extracted and recycled into other materials. The heat generated during this combustion process is converted into electricity by one of two possible methods. The first choice would be a dry high heat turbine, because this is the most efficient method. The second choice could be converting the heat into steam and generating electricity with a steam turbine. Steam turbines are less efficient.

Materials Converted into Energy

As mentioned in the introduction, it is possible to burn any combustible material in our system. Even phenolics and furans can be disposed of through our system. Because the temperature is extremely high and the air in the chamber is super-heated, there are few pollutants left in the air. These pollutants can be dealt with downstream after the heat is extracted to generate electricity. The direct-fired fluidized bed is so different from present garbage-burning systems; there is no comparison in air quality. We plan to run the discharged air from the high-temperature turbine or steam generator through a series of filters and a system to reduce the air to ambient temperature. High temperature air cleaning is accomplished by injecting into the discharged air high-reactive hydrated lime and active carbon for the abatement of heavy metals and dioxins. Ceramic fiber filters are used to filter hot air discharged out of high-temperature turbines. With this method, we will be able to extract dioxins, mercury, lead, and metals so that they can be disposed of properly.

EPA Green House Gas Reduction

EPA has evaluated combustion of garbage and has concluded that there are huge advantages in reducing Green House Gas (GHG) emissions by using garbage disposal through combustion. Combustion of Municipal Solid Waste (MSW) with energy recovery in a Waste-To-Energy (WTE) plant also results in avoided (preventing) CO2 emission in two other industrial sectors. The electricity produced by WTE plants displaces electricity that would be provided by utility plants. Because most power plants in the United Stated use fossil fuels to generate power, there would be a net reduction of CO2. This reduction can be subtracted from any CO2 emission from combustion of MSW. With combustion of MSW, an additional benefit from the recovery of ferrous and non-ferrous metals and glass will occur; they can be recycled. Recycling of material takes less energy, so less CO2 is generated, and this is rated as a reduction of GHG by EPA. One of the largest contributors to the reduction of GHG is Small-Waste-To-Energy (SWTE) plants. The two greatest benefits from SWTE plants are waste materials don't need to be hauled long distances, and CO2 emissions are reduced. Also, because ash is disposed of easily by mixing it with concrete, an additional reduction of CO2 results. EPA converted the 0.11 pounds of non-biomass carbon per pound of mixed MSW to units of metric tons of carbon equivalent (MTCE) per ton of mixed MSW combusted. The resulting value for mixed MSW is 0.10 MTCE per ton of MSW combusted material. The results of SWTE plants are 0.01 MTCE per ton of MSW because of the reduction in CO2 emissions saved by not having to transport MSW and ash long distances. Avoided CO2 emission by combustion of MSW at SWTE plants is the net reduction of .26 MTCE per ton of material input ("Greenhouse" 81).

The energy content of mixed MSW generates 5,000 BTU per pound of MSW combusted. This translates into a net value of 550 kWh generated per ton of mixed MSW. There are 544 kWh per ton delivered by SWTE plants because of energy losses through transmission ("Greenhouse" 86).

Landfills contribute .26 MTCE/ton of GHG per ton of MSW because they release methane gas. This could be reduced by collecting the methane gas and using it as a fuel. There is still a negative because of the CO2 emission created by burning methane gas. Burning methane gas reduces emissions by.18 MTCE per ton of MSW, but there are still releases of GHG at 0.08 MTCE/ton of GHG emissions. There is the addition of .10 MTCE/ton of GHG because of the CO2 generated by transporting MSW to landfills. The net generation of GHG equals 0.18 MTCE per ton of MSW ("Greenhouse" 82).

Collection of Pollutants

We then plan to collect the CO2 and run it through a low pressure compressor and pump it into an injection well. This is technology used in the oil industry. CO2 can be successfully injected into sandstone, limestone, dolomite, and cherts (rock consisting essentially of cryptocrystalline quartz). There isn't any limitation to the depth of injection wells. The depth that CO2 will permeate is different for each material and ranges from 8 to 600 feet. Minimum depth of wells should be based on material available in the injection well (see Figure 2).

Figure 2. Line diagram of complete system layout.
Source: Created by Melvin Fiegi

Disposal of Ash and Fly Ash

The present technology allows ash to be mixed with concrete. Ash strengthens concrete and can be used in buildings, bridges and highways ("Waste"). Also, ash is used in cinder blocks. The fly ash collected can be used in sheetrock, roofing tile, and a special insulation product. By disposing of these materials this way eliminates the hauling of ash to landfills. This would be especially desirable on islands or in small countries with landfill problems.

Future Fuel Plans

An additional benefit will be the adaptability of our system to hydrogen fuel. The U.S. Department of Energy is working with industries, national laboratories, and academics to expedite the development of hydrogen technologies. The picture below shows a 16-tube storage trailer used by the California Department of Transportation. The trailer stores 104,000 cubic feet of hydrogen at 3130 psi. The two tubes on the ground store 12,500 cubic feet of hydrogen at 4000 psi (Figure 3).

Figure 3. Hydrogen fuel storage tanks.
Source: Clapper

The SunLine Company was tapped by the U.S. Department of Energy to coordinate several projects designed to advance the commercialization of hydrogen as a transportation fuel. In April 2000, they built the first hydrogen generation/storage/ fueling facility for public transportation. Hydrogen is 50% more powerful than gasoline. With the present technology, we could use a fuel called Hythane that SunLine created. The Hythane fuel is a blend of 80% compressed natural gas (CNG) and 20% hydrogen. This fuel operates the first zero-emission fuel cell bus. The hydrogen used in this process is generated by solar electricity that operates an electrolyzer. The electrolyzer separates the hydrogen and oxygen from water. They are working on a project now to use the electricity from a wind turbine to operate an electrolyzer (Clapper).

Interview

City of Portland- Energy Division
Office of Sustainable Development
Curt Nichols, Senior Energy Manager

Curt Nichols stated that the most important part of the business we've planned is the waste-to-energy process. He recommended that we have detailed information on how we were going to remove pollutants and toxins from the discharged air. We talked about what would be the most important materials that needed to be recycled, and he suggested that tires and electronic waste were key items. Also, he stated that EPA and DEQ are the two biggest hurdles we would have to conquer, but by running air quality tests and having EPA and DEQ analyze the results, it could be overcome.

What is interesting is he stated that waste-to-energy isn't classified as recycling. He said that our product in the state of Oregon would qualify for Oregon's Pollution Control Tax Credit of up to 50% and also a Business Energy Tax Credit of 35%. Curt stated that we should get certified to burn hazardous waste materials because this would add a very important feature to our equipment. He also suggested that we add stack-burner pollution control to our product line because of the problem with pollutants emissions from smokestacks (Nichols).

Curt thought that if we really wanted to get into a gold mine, we should come up with a method for disposing of asbestos. He said there is a multi-million dollar business in asbestos disposal (Nichols).

Possible Competitor

Gem Gas Conversion Technology

This company uses a pyrolysis (chemical change brought by the action of high heat) process which is the conversion of organic material to gas. Solid dry fuel (any combustible material with less than 5% moisture) is put into a converter chamber that operates at a high temperature. The gas given off by the process is similar to natural gas. This gas is used as a fuel to generate steam which is used to produce electricity. However, several problems occur with the system. The fuel used can't have over 5% moisture in it to work properly, so if they use garbage it will need to be dried. There can't be any contaminants like glass or metal, because these materials hinder the gasification process. All materials introduced into the chamber have to be 25 mm X 25 mm, so any garbage introduced into the process must be ground up. The chamber doesn't have any way to fluidize the material, so once the material reaches the bottom of the chamber, it won't burn completely. The company has suggested that they are going to recycle tires, but they need to grind up the tires first. Grinding up tires is not a practical way to convert them to energy. It takes almost as much energy to grind up tires as the energy that will be recovered. The pyrolysis system isn't an efficient method of generating electricity from tires. It costs $750 per hour to operate a tire-grinding machine that grinds tires down to 25 mm X 25 mm. The tire grinding machine costs $2.2 million dollars. Why spend this kind of money when whole tires can be burned in a fluidized bed? This process just isn't cost effective because the garbage has to be dried to no more than 5% moisture content, the garbage then has to be ground up, and it can't contain any glass or metal (Weltz).

Waste Generation Charts

This chart indicates how much waste we generate in the United States per year. It shows that all garbage can't be burned. If all garbage is run through a waste-to-energy plant, all recyclable materials would be separated. Some items could be composted, and the balance could be burned to create energy (Figure 4).

Figure 4. Waste Generation
Source: "Basic"

This chart in Figure 5 reveals that the garbage generated per person in the U.S. has been growing for the last 40 years. With our technology, much of this waste could be converted into energy.

Figure 5. Waste Trends
Source: "Basic"

Waste Recycling Charts

This chart shows that the rate of recycling is increasing. With our system it is possible to recycle over 90% of the garbage generated. We can accomplish this by converting garbage into energy by fluidized burning.

Figure 6. Waste Recycling
Source: "Basic"

Figure 7 shows six materials that could be recycled at a rate of over 90%. They are auto batteries, steel cans, yard trimmings, aluminum beer and soft drink cans, and glass containers. The balance of the materials can be converted to electricity by fluidized combustion waste-to-energy recycling.

Figure 7. Recycling Rates
Source: "Basic"

CONCLUSION

The research proves that the waste-to-energy process is very practical. It has been shown that scrap tire disposal is best accomplished by fluidized bed combustion. Fluidized beds can be operated efficiently and pollution free. With this technology, scrap tires can be converted to energy with no pollution. Another huge benefit is being able to reduce garbage down to ash which can then be used in other processes. By building small waste-to-energy plants in rural areas, garbage won't need to be hauled long distances. The same applies when building large waste-to-energy plants in metropolitan areas. EPA gives credit to facilities that reduce CO2 emissions because garbage is only hauled short distances. Also, it is possible to build these plants so that no pollution is emitted and CO2 is reduced considerably. It has been shown that ash can be disposed of several different ways. It can be added to concrete to strengthen it for constructing bridges, buildings, and highways and also can be used in cinder blocks. The fly ash can be used in roofing tile, sheetrock, and insulation.

An additional advantage is that the system can be changed over to hydrogen fuel to reduce pollution even more. A wind turbine-operated electrolyzer could be set up in eastern Oregon to generate hydrogen fuel for our systems. Curt Nichols, a senior energy manager, felt that our idea of converting waste-to-energy is the best way to dispose of garbage and scrap tires. He also suggested that we research ways to dispose of asbestos. Research has shown that pyrolysis is not a viable method of processing garbage or tires. This process is costly because of the high amount of energy needed to prepare the materials to be used in the process. The most practical and efficient way to convert garbage and scrap tires into energy is fluidized-bed combustion which is a pollution-free process.

SOURCES CITED

"Air Emissions From Scrap Tire Combustion." 12/10/2002. U.S. Environmental Protection Agency. 02/12/2003. <http://www.epa.gov>.

"Basic Facts." 02/11/2003. U.S. Environmental Protection Agency. 02/12/2003. <http://www.epa.gov/epaoswer/non-hw/muncpl/facts.htm>.

Clapper, William L., Jr. "Hydrogen Commercialization for the 21st Century". 01/23/2003. U.S. Department of Energy Online. 02/17/2003. <http://www.eere.gov/hydrogenandfuelcells>

"Environmental News." 02/11/2003. U.S. Environmental Protection Agency. 01/12/2003. <http://www.epa.gov/admpress.htm>

Foundry Automation Inc. Advertisement. 11/20/2002.

Goodrich, Melissa. "Bring it On ." Dec. 2002. Recycling Today. 02/17/2003. <http://www.recyclingtoday.com>.

"Greenhouse Gas Emissions." 02/11/2003. U.S. Environmental Protection Agency. 02/12/2003. <http://www.epa.gov>.

Nichols, Curt. Senior Energy Manager. Personal interview. 01/19/2003.

"Oregon Toxic Release Inventory." 02/11/2003. U.S. Environmental Protection Agency. 02/12/2003. <http://www.epa.gov/epaoswer/hazwaste.htm>.

"Tire-Burning Furnace Gets Sparks." Scrap Tire News Online. 12/10/2002. <http://www.scraptirenews.com>

"Waste to Energy." 02/04/2003. Energy Information Administration. 02/17/2003. <http://www.eia.doe.gov>

Weltz, Doug. Gem Gas Conversion Technology. 10/30/2002. 11/15/2002. dweltz@earthlink.net

Nominated by Jim Grabill, English Department