KR19980020545A - Pellet-type solid fuel extracted from waste, manufacturing method thereof, and method for operating solid fuel combustion rod using the solid fuel - Google Patents

Abstract

This paper introduces the use of waste extraction materials that improve performance with fixing agents that can significantly reduce contaminants such as acid gases, especially SO ₂ and NOx, and toxic substances, especially polycyclic aromatic hydrocarbons and polychlorinated biphenyls. Oxidizing material and sulfur-containing particulate fuel are introduced into the combustion section of the solid fuel combustion furnace. Particulate fuel contains 10% or more of compressed RDF pellets containing alkaline soil metal hydroxides, especially calcium hydroxide as a binder. Using a fixing agent an amount sufficient RDF pellets when the SO ₂ content of binder is not added RDF pellets is at least 20% lower exhaust gas is generated in the combustion section than the SO ₂ content of the same amount as contained in its class-fuel mixture to heat the reference . The polycyclic aromatic hydrocarbon content of the combustion exhaust is at least 30% lower than equivalent fuels containing the same amount of RDF pellets on a caloric basis. The polychlorinated biphenyl content of the exhaust gas is also at least 50% lower than without the calcium hydroxide binder. Also disclosed is a method of producing compressed RDF pellets, in which a mixture of fine calcium hydroxide and RDF fluff is injected through an injection die at a temperature of 140-190 ° F. and an injection time of 2-10 seconds.

Description

[Name of invention]

Pellet-type solid fuel extracted from waste, manufacturing method thereof, and method for operating solid fuel combustion rod using the solid fuel

Detailed description of the invention

Background of the Invention

The waste extract fuel (RDF) of the present invention refers to a product produced in a solid waste treatment plant, which processes solid waste or industrial solid waste from municipalities in order to significantly reduce the amount of waste eventually landfilled. It is a product that can be used as a single or main fuel in power plants, steel mills, boilers, or mixed with other hydrocarbon fuels such as coal.

Until now, waste extraction fuels were stored in compressed pellets and stored and then used as fuel in the combustion process. However, this invention removes too small or too large material as raw waste passes through the grinding and filtration system, resulting in an intermediate product and then feeding the material into the air classifier. An air classifier separates relatively light materials, such as paper and plastic, from heavier materials such as metal or glass. Light materials pass through the cutter and the compressor and then enter the dryer, where the moisture content is reduced to about 17%. The material discharged from the dryer can be mixed with coal dust in a mixing ratio of about 25-50% by weight. When the mixture of coal and waste is fed into a compressor and pelletizer system, the mixture is fed into a rolling mill and injection molded through a die screen to produce compressed RDF pellets.

Fixing agents may also be added to the waste extract fuel to produce higher compressive RDF pellets. There is also a binder / fly ash system, as well as the addition of coal powder to increase the calories of the raw materials. Waste materials are generally suitable for solid cellulose materials such as paper or cardboard, plastic materials such as styrofoam and soft plastics, soft metal waste such as paper clips and staples, and solid wastes such as glass, corn starch, portland cement and asphalt emulsions. , And lignin and the like. RDF is molded into cylindrical or square pellets with a diameter of about 3/4 inch, a length of about 3/4 inch, a dry compressive stress of about 30 psi and a dry moisture of about 10% by weight. The calorific value of the RDF pellets produced is in excess of about 6000 BTUs per pound and can be used as the main fuel and auxiliary fuel.

As explained earlier, waste extract fuels can be used as a single fuel source or co-fuel with fossil fuels such as coal. One advantage of waste extract fuels is that the sulfur content is usually less than 0.25% and relatively low, even below 0.5%. On the other hand, the sulfur content of coal is relatively high, and as a result, measures to reduce the emission of sulfur are needed when burning coal. A well-separated lime, limestone, or mixture of dolomite and fly ash is mixed with the coal dust and used as a binder that can form coal or pellets. The processing method is a method for replacing the liquefied combustion processing in which pulverized coal is burned in the presence of a substance such as limestone or dolomite to change sulfur dioxide into a solid calcium sulfite sulfate containing a reaction product. Lime itself is a binder component that functions as a binder, and also acts to make volcanic cement, and also acts as a desulfurizer during combustion. Lime and coal ash have a well-divided powder form that is evenly distributed throughout the coal dust, thus maximizing cement formation. Fixings that look like cement decompose during combustion, producing lime and coal ash again in the combustor. The well separated lime can then be used for in-furnace desulfurization of the combustion gas, using finished and inoperative lime particles which are discharged out of the combustor as suspended dust.

Another method that can be used to improve coal is to produce compressed coal pellets that retain moisture from the lignite and improve calories, in which the lignite is pulverized by cutting to form wet calcined mass and injected into the pellet. do. When in the liquid state during plasticization, sodium carbonate is added to enhance the strength of the compressed product. Alkaline metal carbides in the soil can also be used, and the effect is doubled by the addition of magnesium hydroxide and calcium hydroxide to increase the pH of the acid coal while forming an electrostatic bridge binding state using acidic substances on the surrounding coal particles. It can increase. Specifically, for example, the addition of 5% magnesium hydroxide resulted in an average compressive strength of 61 MPa as opposed to 11 MPa of pellets without added additives. In addition, addition of 2% and 5% calcium hydroxide resulted in compressive strengths of 39 and 65 MPa, respectively.

Summary of the Invention

Based on the invention to date, a method for using RDF pellets with improved performance as a binder that significantly reduces acid gases such as SOx and NOx and pollutants, in particular polycyclic aromatic hydrocarbons and polychlorinated biphenyls, has been developed. You can find it. When using this invention, the particulate fuel containing an oxidant and sulfur is supplied to the combustion part of a solid fuel furnace. Particulate fuel contains 10% or more of compressed RDF pellets, which contain alkaline metal hydroxide found in soil as a binder. Combustion conditions are established in the furnace and then particulate fuel is burned in the presence of oxidants. When a sufficient amount of alkaline metal hydroxide found in the soil is supplied, combustion emissions of at least 20% lower SO ₂ content than comparable fuel mixtures containing the same amount of RDF pellets on a caloric basis but do not contain alkaline soil metal hydroxides Produce gas If possible, the fuel is preferably a mixture of RDF pellets and sulfur containing fuels, which should contain at least 15% of RDF pellets containing alkaline soil metal hydroxide binders. According to another aspect of the present invention, the polycyclic aromatic hydrocarbons content of the exhaust gas discharged from the combustion unit is equivalent to that of RDF pellets added on the basis of calories but does not contain alkaline soil metal hydroxide fixing agent. At least 30% lower than fuel. As another aspect of this invention, the polychlorinated biphenyl content of this off-gas is at least 50% lower than the polychlorinated biphenyl content in the absence of an alkali metal hydroxide fixing agent.

Fixing agents for RDF pellets are preferably calcium hydroxide if possible. The content of calcium hydroxide depends on how much moisture is in the RDF fluff, which is the preliminary stage of the pellet. The more moisture, the more calcium hydroxide is needed. In many cases, a suitable calcium hydroxide content is on the order of 4-10% by weight. However, when mixing RDF pellets, which have improved performance as a fixing agent, with coal having a very high sulfur content, pellets having a calcium hydroxide content of more than 10% by weight may be used. Such pellets may contain 11-25% calcium hydroxide in weight proportions, preferably 12-20% calcium hydroxide.

Another aspect of this invention is a method of producing compressed RDF pellets. Particulate calcium hydroxide with an average particle size of less than 0.5 mm (35 US sieve size) is added to an RDF fluff whose moisture is in the range of 10-50% by weight. A mixture of finely added calcium hydroxide is mixed well to produce a product with evenly spreading calcium hydroxide throughout the fluff and relatively low contact. This mixture is then passed through an injection system where the mixture is compressed and pelletized. At this stage, the mixture passes through an injection die with an injection diameter ranging from 1 / 2-1 inch. The fluff mixture containing calcium hydroxide is injected through an injection die with a temperature of 140-190 ° F. and a passage time of 2-10 seconds. If possible, the injection diameter should be about 3/4 inch and the transit time should be about 3-5 seconds at 150-170 ° F.

[Detailed Description of the Invention]

Waste extract fuels, as we have seen, are products that recycle and process solid waste from municipalities that are usually landfilled, and sometimes industrial solid waste. Municipal solid waste is mainly cellulose materials such as paper, cardboard, wood, grass, and some food waste and plastics. Small amounts (15-30%) of inorganic materials, such as metals and glass, are also found in municipal solid waste.

A variety of processing methods are used in the manufacturing process to produce waste extract fuels. Usually, when solid waste arrives at a treatment facility, bulky or hazardous items such as electrical appliances, mattresses, and car batteries are separated from the waste. The waste is then screened to remove small organics and then sorted for recycling by hand, usually aluminum, glass and cardboard. After grinding, the waste is passed through a magnetic separator to remove ferrous metals and sent to dust collectors and other suitable air classifiers. After crushing again, a low density 'fluff' is produced. The material is so dense that it only weighs a few pounds per square foot and can be burned in an air-suspension combustion section. Usually, however, the lint is compressed and pelleted to produce solid pellets with a density of 20-40 pounds per square foot. At the end of the grinding process, the moisture in the fluff will be about 10-40% by weight, usually 20-30%. The main component of the fluff is of course cellulosic material and there are some other organic materials and plastics.

Fixing agents can be used to make RDF pellets to improve the density and integrity of the RDF pellets. Unlike generally homogeneous coal powders with a narrow range of size distributions, RDF fluff has a low density mass of heterogeneous particles with a wide range of sizes and non-uniform shapes. Therefore, in the case of improving the performance with a fixing agent in the production of RDF pellets, the fixing agent is usually in the form of an oily cement such as Portland cement or in an organic state such as lignin or corn starch.

The present invention uses alkaline soil metal hydroxides as a binder for compressed RDF pellets. Preferred alkaline soil metal hydroxides are calcium hydroxide and the use of calcium hydroxide as a performance improving fixer for RDF pellets will be discussed in detail. However, other alkaline soil metal hydroxides may also be used. For example, alkaline earth metal hydroxides containing both calcium hydroxide and magnesium hydroxide extracted from dolomite can be used as a fixing agent. Alkaline soil metal hydroxides other than calcium hydroxide and magnesium hydroxide may theoretically be used as the fixing agent of the present invention, but those experienced in this field agree that the use of such materials is practically inadequate for economic and other reasons. do. Improving Adhesion Performance There are several factors to consider when determining the amount of calcium hydroxide or other alkaline soil metal hydroxides added to RDF fluff during formation of pellets. As will be explained in more detail later, it is desirable to add calcium hydroxide to the RDF fluff in the form of finely ground dry powder. Water should not be added deliberately to calcium hydroxide, lint or final mixture to produce plastic material as it does during some RDF benefication processing. Usually at least 2% calcium hydroxide is used by weight, which means that 2% calcium hydroxide is used in 98% RDF fluff by weight. If the moisture of the RDF fluff becomes high, it is generally desirable to increase the amount of calcium hydroxide fixing agent. Most RDF fluff has at least 20-30% moisture inside, and 2% calcium hydroxide is enough for water alone. However, some fluff moisture is 40-50% and in this case calcium hydroxide should be 6-10% or more by weight.

When preparing RDF pellets with improved performance as a binder, it is important to mix calcium hydroxide and lint well so that the calcium hydroxide spreads well throughout the lint and close contact between the lint and calcium hydroxide. If possible, grind calcium hydroxide so that the average particle size is less than 0.5 mm. To prevent excessive amounts of suspended dust during the manufacturing process, the particle size of calcium hydroxide should not normally be less than 0.04 mm (size over 400 US sieves). Both batch unit mixing or continuous mixing can be used to produce a mixture of calcium hydroxide and fluff, but in practice it is preferable to use a continuous mixing method. For example, well separated calcium hydroxide can be added to the RDF fluff by gravity feeding from a surveyed hopper to a screw conveyor with a slope of about 30-45 degrees. When the fluff-calcium hydroxide mixture moves along the conveyor, it is mechanically shaken and flipped, causing the calcium hydroxide to mix evenly throughout the fluff.

At the top end of the conveyor, the mixture falls by gravity into a hopper for the pelletizer, which can be a rolling mill in a rotating die screen. The method of injecting a fluff / calcium hydroxide mixture into the injection die by die screen or other suitable method plays an important role in imparting the desired properties to the pellets. Factors affecting the properties of the pellets include the length of the injection passage (thickness of the die screen wall), the injection diameter (diameter of the injection passage within the die screen), and the injection temperature (flux / calcium hydroxide mixture passes through the die screen. Temperature at the time of use). Usually, if the injection temperature is too high, the injection time is too long or the injection diameter is too small, there is a high probability of the injection machine clogging. On the contrary, however, if the injection temperature is too low, the injection time is too short or the injection diameter is too large, the density and performance of the pellets will not reach the desired level. If possible, the injection diameter should be 1 / 2-1 inch and the injection diameter should be about 3/4 inch, which is believed to give the best results. The injection temperature is kept in the 140-190 ° F range if possible and the best temperature is 150-170 ° F. Injection time should be within 2-10 seconds, preferably 3-5 seconds if possible.

Increasing the amount of calcium hydroxide generally results in an increase in the density of the RDF pellets improved with a binder until the amount of calcium hydroxide is about 10%. If the amount of calcium hydroxide is higher than that, the density of the pelleted product is lowered. Therefore, in view of the improvement of performance through the fixing agent, the addition of 10% calcium hydroxide is considered to be the upper limit. However, as will be seen later, increasing the content of calcium hydroxide has the effect of reducing the amount of undesirable or toxic emissions in certain applications of the present invention.

To date, RDF pellets have been used as co-fuel with particulate coal in solid fuel combustion furnaces such as in power plants. Pollutants emitted from such furnaces include acid gases, SOx, and NOx, which cause so-called acid rain and polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB).

When burning the RDF-coal mixture, SOx (usually sulfur dioxide, which may have some sulfur trioxide) is mainly released from coal. In this regard, the sulfur content of RDF pellets is relatively low, usually 1/4%, up to 1/2%. The sulfur content of coal is usually considerably higher than this, which may be 2 1/2% or higher. Therefore, the main cause of SOx emissions is sulfur contained in coal, and in the case of a mixture of coal and RDF pellets, SOx emissions are expected to decrease as the amount of RDF pellets in the mixture increases.

NOx pollutants (nitrogen oxides and nitrogen dioxide) come from coal and RDF pellets and nitrogen compounds in the air and nitrogen molecules in the air. Nitrogen-containing compounds are found in both coal and RDF pellets but usually have higher nitrogen content. NOx generated from nitrogen molecules in air depends directly on the combustion temperature, and the higher the temperature, the more NOx is produced. In this situation, it would normally be expected that NOx emissions and SOx emissions would be reduced as the amount of RDF mixture in the coal increased.

Polycyclic aromatic hydrocarbons (PAH) emitted during solid fuel combustion include compounds containing about 2-7 aromatic rings, usually with a high density ring structure. Polycyclic aromatic compounds such as benzo-a-pyrene and methylcholanthrene are carcinogenic. Substances such as naphthalene and anthracene are not carcinogenic. Polycyclic aromatic hydrocarbons contained in the combustion products, measured in the experiments described below include naphthalene, acenaphthylene, benzo-a-anthracene, chrysene, acenaphthene, benzo-a-fluoranthene, fluorine, benzo-k-fluoranthene, phenanthrene, benzo-a-pyrene, anthracene, dibenzo-a, h-anthracene, fluoranthene, benzo-g, h, i-perylene, pyrene and indendo-1,2,3-c, d pyrene. Polycyclic aromatic compounds arise from the use of coal or RDF because they are produced during the incomplete combustion of hydroxides during combustion.

The properties of polychlorinated biphenyls can be represented by the following generalized formula:

C ₁₂ H _m Cl _n (1)

In the formula: the sum of m and n is 10 and n is at least 1. The PCBs in the combustion emissions are produced from the corresponding substances contained in the combustion and also as the combustion products of hydroxides from various sources in the presence of chloride.

Calcium hydroxide, which is used as a fixing agent in the manufacture of compressed RDF pellets according to the present invention, reduces SO ₂ emissions, as well as NOx, HCl and CO ₂ emissions, and also reduces the emissions of polycyclic aromatic hydrocarbons and polychlorinated biphenyls. Experiments conducted in connection with the present invention initially showed that calcium hydroxide binders were effective in inhibiting contaminants only in coal-RDF pellet mixtures containing 10% RDF pellets on a caloric basis. In particular, the initial results of this experiment showed that it was effective in inhibiting SO ₂ in a mixture with 10% RDF pellets and 90% coal, but was not effective when the RDF content was raised to 20%. It was not clear whether the fixer had the effect of inhibiting the NOx content. Some tests showed an inhibitory effect at 10% and 20% RDF pellet content, whereas no other effect was found.

Regarding the content of polycyclic aromatic hydrocarbons, the first data showed an excellent inhibitory effect on RDF-coal mixtures containing 10% RDF, but as the RDF content increased to 20%, the binder actually increased the emissions of PAH. Showed.

However, after analyzing the results of these experiments, the higher utilization rate of RDF pellets, especially when increasing the RDF pellet content by 20% and 30% and up to 50% on a calorie basis, resulted in undesirable contamination of the calcium hydroxide binder. It has been shown to be effective in reducing the content of the substance.

(Note: * 1. Unless otherwise specified, the relative content of RDF pellets and coal is based on calories, so there are RDF pellets with calories of 7,000 BTU and coal with calories of 11,000 BTUs per pound. For example, mixtures containing 10% RDF pellets and 90% coals, based on calories, contain about 15% RDF and 85% coal.)

The use of binders in fuel mixtures with high RDF content could significantly reduce the SO ₂ content, although NOx was not reduced, but the binder had no detrimental effect. However, the use of binders in fuel mixtures with high RDF content could significantly reduce the PAH and PCB content.

During the experimental work on the present invention, a total of 300 tonnes of RDF pellets in a boiler furnace, one of five furnaces meeting the steam requirements of the Argonne National Laboratory, Argonne, Illinois, was co-fueled with high sulfur content coal. Burned. The boiler's rated steam capacity per hour was 170,000 pounds with a maximum gauge pressure of 200 psig.

The boiler furnace had air pollution control equipment consisting of several dust collectors in series, lime spray dry absorbers, and fiber filter bag houses. Furnace emissions are first moved to several dust collectors, where particulates are removed and then sent to a spray dryer. The contact of the exhaust gas with the lime feed slurry in the spray dryer absorbs sulfur dioxide and cools the exhaust gas. According to the design specification of the spray drying absorber, at least 78.3% of the sulfur dioxide in the exhaust is removed. Some of the dry matter passed through the dryer, such as coal ash, calcium sulfite and sulfate, and unreacted lime molecules, falls to the bottom of the absorption chamber. Cooled exhaust gas discharged from the spray drying absorption system then passes through a filter bag module where residual coal ash and other particulate matter are filtered. Exhaust samples were manually taken at three locations during the experiment: Site 1 was in a combustion section with a temperature of about 1200 ° F., and site 2 was between several dust collectors and spray dryer modules, with a temperature of about 320 ° F. Site 3 was a chimney with a temperature of about 170 ° F after passing through all decontamination units.

The RDF pellets used in the experiment were pellets obtained from only two sources, referred to as manufacturer A and manufacturer B, using pellets without a binder and pellets containing 4% and 8% calcium hydroxide binders by weight, respectively. It became. The pellets were mixed with high sulfur content at 10%, 20%, 30% and 50% ratios on a caloric basis. The coal used in the experiment was a high sulfur content Kentucky coal with a sulfur content of 2.7% on receipt (about 6.3% moisture) and a sulfur content of 2.88% on drying. The average calorific value of coal was 11,200 BUTs per pound at the time of receipt.

The sulfur content of the RDF fuel pellets was about 1/4% by weight. The calorie of manufacturer A pellets was about 7500 BTU / lb and the manufacturer B pellets was about 7000 BTU / lb. Manufacturer A pellets generally have higher homogeneity of the raw materials and better integrity than the manufacturer B pellets. In addition, the actual binder content of the pellets of manufacturer A was closer to the official binder content than the pellets of manufacturer B.

In the reporting of the experiments, the coal-RDF pellet mixture or the coal itself was classified into 12 types according to the increase or decrease of single coal or RDF content, and the names of the first to 12 experiments were named. These experiments are summarized in Table I by the coal-RDF pellet content (calories), the calcium hydroxide content by weight ratio and the approximate length of the experiment in hours. In two experiments, the 9th and 10th experiments, RDF fluff, the raw material for pellet production, contained less plastic. The pellets used in the rest of the experiment contained unmodified plastic, as received at the municipal solid waste resource recovery plant.

TABLE I

The characteristics of each experiment number are shown in Table II in more detail according to the experimental sequence. The manufacturer of the RDF pellets is also labeled A or B as described above. In Table II, the beginning and end of the experiment are marked with S and E, respectively. As shown in Table II, the first and twelfth experiments (only coal) were actually separated from each other with other experiments using a coal-RDF pellet mixture in between. Particularly in the 12th experiment, the analytical results discussed below may differ from the reality by experiments with RDF pellets in the fuel that were conducted earlier.

TABLE II

During the experiment, SO ₂ , NOx, HCl, polyaromatic hydrocarbons and polychlorinated biphenyls were analyzed for samples taken at sites 2 and 3.

As will be appreciated by those skilled in the analytical technique, the sample taken at site 2 while passing through the emission filtration module more accurately reflects the amount of pollutant in the combustion exhaust gases than at site 3. In this regard, even if a plurality of dust collectors are treated with combustion exhaust gas to remove particulates, there is practically no effect on SO ₂ , NO x, CO ₂ or HCl contained in the exhaust gas. Polychlorinated biphenyls and polyaromatic hydrocarbons are virtually vapor when passing through multiple scrubbers, so only a small amount of these materials would have been removed in the first stage exhaust filtration module. It is believed that these materials can only be condensed and absorbed as particulates when the temperature of the exhaust gas drops below 300 ° F. Therefore, the evaluation of the experiments was based on the assumption that the amount of polyaromatic hydrocarbons and polychlorinated biphenyls actually removed from multiple dust collector modules would not exceed 10-20%.

Acid gas was collected from the flue-gases using a Anderson Model 300 gas sampler and ion chromatographed using a Dionex Model 2010 I ion chromatograph. Trapping reagents used in the sampler were, in most cases, by weight 2% sodium hydroxide solution, 2% aqueous sodium hydroxide solution and 4% calory permanganate. In some cases, other reagents were used as indicated in Table IV below. When collecting HCl is considered to be a 2% sodium hydroxide solution is shown the best results, it is considered that a 2% sodium hydroxide, 4% potassium permanganate solution was most effective in the collection of SO ₂ and NOx. As shown in Table III, the relative effects of these two reagents are shown as comparative samples taken about 3 hours apart at site 2 of the ninth experiment.

TABLE III

Table IV shows the contents of HCl, NOx, and SO ₂ in the exhaust gases collected at sites 2 and 3 during the experiment. The data in Table IV tracked the change as the RDF pellet content increased.

Table IV

Table IV (continued)

The use of calcium hydroxide binders in accordance with the present invention also reduces carbon dioxide emissions. Compared to coal-RDF pellets containing 4% calcium hydroxide and equivalent fuels containing the same amount of RDF pellets on a caloric basis, but without the fixing agent in the pellets, Carbon dioxide is reduced by at least 5% by weight. For coal-RDF pellets containing 8% calcium hydroxide binder, the resulting reduction in carbon dioxide is at least 20% by volume. Table V shows the average carbon dioxide content in the exhaust gas collected at site 2 during the experiment. The data in Table V are for the proportions of RDF pellet mixtures of 10%, 20% and 30% and the calcium hydroxide fixing agent concentrations of coal at 0%, 4% and 8% by weight. The reference value for a single coal burned without mixing RDF pellets was 9.1%.

TABLE V

Average CO ₂ Content by Volume

* Means are based on one test.

The polyaromatic hydrocarbons and polychlorinated biphenyl emissions observed during the experiment are shown in Tables VI and IV. The results of analysis of samples taken at site 2 are in Table VI, and the results of analysis of samples taken at site 3 are in Table VII. Of course, the sample taken at location 2 more accurately reflects the PAH and PCB content contained in the combustion flue gases.

Table VI

[Table VII]

As described above, RDF pellets of manufacturer A are generally more homogeneous in content than manufacturer B pellets. In addition, the analysis of the A-type pellets showed that the calcium hydroxide concentration of the pellets was closer to the official calcium hydroxide concentration than the B-type pellets. In addition, the pellets of manufacturer A gradually increased in density with increasing calcium hydroxide content. The mean density of the pellets of the manufacturer A fixing agent was not contained was ³ 42.0ℓb / ft, the average density of the calcium hydroxide fixing agent containing 4% of pellets are contained 43.3ℓb / ft ^3, and the calcium hydroxide fixing agent 8% The average density of the pellets was 45.7 Lb / ft ³ . On the other hand, manufacturer B pellets did not show this association. In the absence of a binder, the average density at the calcium hydroxide content of 4% and the calcium hydroxide content of 8% were 26.8, 25.6, and 26.8 lb / ft ³ , respectively.

In reviewing the data presented above, it can be seen that as the RDF content of the fuel mixture increases, the contents of SO ₂ and NO x decrease. First of all, calcium hydroxide has been shown to be effective in reducing SOx content. This effect is evident in light of the fact that this data is for mixtures with 80% coal and 20% RDF pellets from manufacturer B. When the RDF pellets were 10% and 30%, increasing the calcium hydroxide content to 4% and 8% in the absence of fixing agent showed a significant decrease in SOx emissions.

For NOx emissions, a slight reduction was observed for the 90% coal and 10% RDF mixtures. Some data show that the use of more than 10% of the pellets containing the binder increased virtually NOx emissions. However, a review of manufacturer B's pellets suggests that fuels with a higher RDF content do not show a detrimental effect, even if the binder contained therein has no effect on reducing NOx emissions. As expected, increasing the content of RDF pellets increased the content of HCl because the main source of chlorine was plastics contained in RDF. The fixative seems to have a slight effect on the HCl content until the fuel mixture has an RDF content of about 30%.

Data on coal-only combustion and mixtures with 10% and 30% RDF mix show that calcium hydroxide binders significantly reduce PCB and PAH emissions, considering only the data from manufacturer A pellets. For mixtures containing 80% coal and 20% RDF pellets, site 2 data shows a significant increase in PAH content and 4% to 8% when the binder content proceeds to 4% without binder. It shows a decrease in PAH content as it proceeds. Emissions for 80% calcium hydroxide were significantly higher than those mixtures that still contained no binder.

The use of calcium hydroxide fixing agents increases the ash content, which would eventually be disposed of in any way, so it would be desirable to limit the content of calcium hydroxide fixing agents to 10% by weight. However, when mixing RDF pellets with coal having a relatively high sulfur content, at least 10% of the binder can be used, in which case it is better to use it. In this regard, the sulfur content of coal used for the combustion of power plant furnaces, etc. sometimes represents 3-4% by weight, even higher than 6-7%. In this case, RDF pellets having a calcium hydroxide content of 11% or more can be used as a co-fuel together with coal powder to further reduce the amount of sulfur dioxide generated as sulfur of coal. The calcium hydroxide content can be used up to 25% by weight. When used with high sulfur content, the appropriate calcium hydroxide content is 12-20% by weight.

Having described the specific content of the present invention, those skilled in the art may suggest modifications and attempt to converge all modifications that fall within the scope of the appended claims.

Claims (31)

In the method of operating a solid fuel combustion furnace, the steps are as follows: (a) Particulate fuels containing oxides and sulfur are supplied to the combustion section of the furnace, and the particulate fuels must contain at least 10% by weight calorie of compressed RDF pellets containing alkaline soil metal hydroxide as a binder. (b) Combustion conditions are to be established in the combustion section and the particulate fuel is to be combusted in the presence of oxides. (c) A sufficient amount of alkaline soil metal hydroxide is supplied to the RDF pellets so that the total SO ₂ content of the combustion exhaust gas is equal to the total SO 2 of the equivalent fuel containing the same amount of RDF pellets in calorific units containing alkaline soil metal hydroxides. ₂ At least 20% lower than the content. In Claim Method 1, the fuel should be a mixture of RDF pellets and sulfur containing coal. In Claim Method 2, the particulate fuel should contain at least 20% of RDF pellets, based on calories, containing alkaline soil metal hydroxide as a binder. In claim method 3, the alkaline soil metal hydroxide should be calcium hydroxide. In Claim Method 4, the particulate fuel should consist of 20-50% of RDF pellets containing calcium hydroxide as a fixative and 50-80% of sulfur containing coal based on calories. In Claim Method 5, the polycyclic aromatic hydrocarbon content of the combustion exhaust gas should be at least 30% lower than the polycyclic aromatic hydrocarbon content of the equivalent fuel containing RDF pellets containing no equal amount of calcium hydroxide. In Claim Method 6, the polychlorinated biphenyl content of the combustion exhaust gas should be at least 50% lower than the polychlorinated biphenyl content of the equivalent fuel containing RDF pellets containing no equal amount of calcium hydroxide fixing agent on a caloric basis. In the method of operating a solid fuel combustion furnace, the steps are as follows: (a) It supplies a particulate fuel mixture consisting of oxide, also compressed RDF pellets with added sulfur particles and calcium hydroxide binders, which must be at least 10% mixed in the mixture on a caloric basis. (b) Combustion conditions in the combustion section shall be established and the coal-RDF pellet mixture is combusted in the presence of oxides. (c) A sufficient amount of calcium hydroxide is fed to the RDF pellets so that the total SO ₂ content of the combustion exhaust gas is greater than the total SO ₂ content of the equivalent fuel containing the same amount of RDF pellets containing no amount of calcium hydroxide fixing agent. Keep it at least 20% lower. In Claim Method 8, the polycyclic aromatic hydrocarbon content of the combustion flue should be at least 30% lower than the polycyclic aromatic hydrocarbon content of the equivalent fuel containing RDF pellets containing no equal amount of calcium hydroxide. In Claim Method 9, the polychlorinated biphenyl content of the combustion exhaust gas should be at least 50% lower than the polychlorinated biphenyl content of the equivalent fuel containing RDF pellets containing no equal amount of calcium hydroxide fixing agent on a caloric basis. In Claim Method 8, at least 15% of the particulate fuel on a caloric basis should consist of RDF pellets containing calcium hydroxide as a fixative. In Claim Method 8, the particulate fuel should consist of 20-50% of RDF pellets containing calcium hydroxide as a fixative and 50-80% of sulfur containing coal based on calories. In the method of operating a solid fuel combustion furnace, the steps are as follows: (a) Oxide and particulate fuel are supplied to the combustion section of the furnace, and the particulate fuel must contain at least 10% on a calorific basis of compressed RDF pellets containing alkaline soil metal hydroxide as a binder. (b) Combustion conditions are to be established in the combustion section and the particulate fuel is to be combusted in the presence of oxides. (c) A sufficient amount of alkaline soil metal hydroxide is supplied to the RDF pellets so that the total polycyclic aromatic hydrocarbon content of the combustion exhaust gas is equivalent to that of equivalent fuel containing RDF pellets containing Keep at least 30% lower than the total polycyclic aromatic hydrocarbon content. In claim method 13, the particulate fuel should contain at least 20% of RDF pellets, based on calories, containing alkaline soil metal hydroxide as a fixing agent. In claim method 14, the alkaline soil metal hydroxide should be calcium hydroxide. In claim method 15, the fuel should be a mixture of RDF pellets and sulfur-containing coal and the analysis of the combustion exhaust gases shows that the SO ₂ content is equal to the SO ₂ content of the equivalent fuel mixture containing the same percentage on a caloric basis without the calcium hydroxide fixing agent. It should be at least 20% lower than the content. In Claim Method 16, the particulate fuel should consist of 20-50% of RDF pellets containing calcium hydroxide as a fixative and 50-80% of sulfur containing coal based on calories. In the method of operating a solid fuel combustion furnace, the steps are as follows: (a) Oxide and particulate fuel are supplied to the combustion section of the furnace, and the particulate fuel must contain at least 10% on a calorific basis of compressed RDF pellets containing alkaline soil metal hydroxide as a binder. (b) Combustion conditions are to be established in the combustion section and the particulate fuel is to be combusted in the presence of oxides. (c) supplying a sufficient amount of alkaline soil metal hydroxide so that the total PCB content of the combustion exhaust gases is at least 50 greater than the total PCB content of the equivalent fuel mixture containing RDF pellets containing the same amount of alkaline soil metal hydroxide in calorie units; Keep it low. In Claim Method 18, the particulate fuel should contain at least 20% of RDF pellets, based on calories, containing alkaline soil metal hydroxides as fixing agents. In claim method 19, the alkaline soil metal hydroxide should be calcium hydroxide. In claim method 20, the fuel should be a mixture of RDF pellets and sulfur-containing coal and the analysis of the combustion exhaust gases shows that the SO ₂ content is the SO ₂ of the equivalent fuel mixture containing the same proportions on a caloric basis in the absence of calcium hydroxide binder. It should be at least 20% lower than the content. In Claim Method 21, the particulate fuel should consist of 20-50% RDF pellets containing calcium hydroxide as a fixative and 50-80% sulfur containing coal based on calories. Combustion products are made from a mixture of: (a) RDF pellets having a calcium hydroxide binder of at least 11% and generally no more than 89% RDF fluff components extracted from cellulosic waste, (b) sulfur-containing coal particles having a sulfur content of at least 3% by weight, (c) The amount of lime is at least 20% by weight. Among the components of claim 23, the content range of calcium hydroxide is 11-25%. Of the components of claim 23, the content of calcium hydroxide is at least 12% by weight. Among the components of claim 23, the lime content is at least 20% by weight. In Claim Method 25, the content range of calcium hydroxide is 12-20% by weight. Among the production methods of compressed RDF pellets, the steps are as follows: (a) Particulate calcium hydroxide with an average particle size of less than 0.5 mm is added to an RDF fluff with 10-50% moisture by weight. (b) Mix the mixture made in step (a) well to form a mixture in which calcium hydroxide and lime are in good contact with each other. (c) The mixture of step (b) is sent to an injection system where the mixture is compressed and injected through an injection die having an injection diameter of about 1 / 2-1 inch to form pellets. (d) The mixture of calcium hydroxide and fluff is injected at a temperature of 140-190 ° F and an injection time of 2-10 seconds. In claim method 28, the injection diameter is about 3/4 inch. In claim method 28, the injection time is about 3-5 seconds. In claim method 30, the injection temperature is about 150-170 ° F.