Moisture content limit

Because of the wide variation in composition and properties of brown coal (see Table 3), efficient combustion of these fuels caimot be accomphshed by a single system. The moisture content limits combustion efficiency because some chemical energy is required to convert Hquid water to steam in the flue gases. The steam then increases the dew point of the gases, requiring higher temperatures to avoid condensation in the stack. For fuels up to 25% moisture content, 80% efficiency can be achieved. As the moisture content increases to 60%, the efficiency decreases to 70% and efficiency continues to decline about another 1% for each additional 1% moisture to 70%. 

According to information published by the U.S. Environmental Protection Agency (EPA) in 1994, costs will vary according to the technology chosen and site conditions. As a general rnle, costs go up with increased moisture content. Limitations in the particle size of contaminants and other material handling requirements will also impact applicability and costs at specific sifes (D10895M, p. 4-106). 

First one determines from the material supplier and/or experience, the plastic s moisture content limit. Next determine which procedure will... 

Note that the curves shown in Figures 1 and 2 are confined to the moisture content limits between 6-7 and 24-25%. Measurements below 6 or 7% are not reliable with ordinary moisture meters because the resistance is too high (above 10 ft). 

Heat-water treatment involves exposing starch with low moisture content (18%-27%) to high temperature. Heat-water treatment physieally modifies the starch. The low moisture content limits molecnlar mobility and gelatinization during treatment. Starch that has been heat-water treated has increased gelatinization temperature. 

First, the plastic s moisture content limit is determined. Next, the procedure that will be used in determining water content, such as weighing, drying, and/or reweighing, is determined. These procedures have definite limitations. Fast automatic analyzers, suitable for use with a wide variety of plastic systems, are available that provide quick and accurate data for obtaining the in-plant moisture control of plastics. 

Operating parameters of this German plant, on the basis of one cubic meter of raw gas, iaclude 0.139 m O2, 0.9 kg briquettes, 1.15 kg steam, 1.10 kg feed water, 0.016 kWh, and 1.30 kg gas Hquor produced. Gasifier output is 1850 m /h and gas yield is 1465 m /t dry, ash-free coal. The coal briquettes have a 19% moisture content, 7.8% ash content (dry basis), and ash melting poiat of 1270°C. Thermal efficiency of the gas production process is about 60%, limited by the quaHty and ash melting characteristics of the coal. Overall efficiency from raw coal to finished products is less than 50%. 

Pan and cascade burners are generally more limited ia flexibiHty and are useful only where low sulfur dioxide concentrations are desired. Gases from sulfur burners also contain small amounts of sulfur trioxide, hence the moisture content of the air used can be important ia achieving a corrosion-free operation. Continuous operation at temperatures above the condensation poiat of the product gases is advisable where exposure to steel (qv) surfaces is iavolved. Pressure atomiziag-spray burners, which are particularly suitable when high capacities are needed, are offered by the designers of sulfuric acid plants. 

Equilibrium moisture content is the limiting moisture to which a given material can be dried under specific conditions of air temperature and humidity. 

Equation (12-31) assumes that Df is constant however, Df is rarely constant but varies with moisture content, temperature, and humidity. For long diying times, Eq. (12-31) simphfies to a limiting form of the diffusion equation as... 

Equilibrium moisture content of a solid is particularly important in drying because it represents the limiting moisture content for given conditions of humidity and temperature. If the material is dried to a moisture content less than it normally possesses in equilibrium with atmospheric air, it will return to its equilibrium value on storage unless special precautions are taken. 

Feed Slurry Temperature Temperature can be both an aid and a limitation. As temperature of the feed slurry is increased, the viscosity of the hquid phase is decreased, causing an increase in filtration rate and a decrease in cake moisture content. The limit to the benefits of increased temperature occurs when the vapor pressure of the hquid phase starts to materially reduce the allowable vacuum. If the hquid phase is permitted to flash within the filter internals, various undesired resiilts may ensue disruption in cake formation adjacent to the medium, scale deposit on the filter internals, a sharp rise in pressure drop within the filter drainage passages due to increased vapor flow, or decreased vacuum pump capacity. In most cases, the vacuum system should be designed so that the liquid phase does not boil. 

In a combined cycle plant, high steam pressures do not necessarily convert to a high thermal efficiency for a combined cycle power plant. Expanding the steam at higher steam pressure causes an increase in the moisture content at the exit of the steam turbine. The increase in moisture content creates major erosion and corrosion problems in the later stages of the turbine. A limit is set at about 10% (90% steam quality) moisture content. 

The data presented in Figure 19.7 were obtained on a Sonntag-Universal machine which flexes a beam in tension and compression. Whereas the acetal resin was subjected to stresses at 1800 cycles per minute at 75°F and at 100% RH, the nylons were cycled at only 1200 cycles per minute and had a moisture content of 2.5%. The polyethylene sample was also flexed at 1200 cycles per minute. Whilst the moisture content has not been found to be a significant factor it has been observed that the geometry of the test piece and, in particular, the presence of notches has a profound effect on the fatigue endurance limit. 

Applicability/Limitations Liquid injection incineration can be applied to all pumpable organic wastes including wastes with high moisture content. Care must be taken in matching waste (especially viscosity and solids content) to specific nozzle design. Particle size is a relevant consideration so that the wastes do not clog the nozzle. Emission control systems will probably be required for wastes with ash content above 0.5 percent (particulate control) or for halogenated wastes (acid gas scrubbers). 

If a gas is compressed, its absolute moisture content is reduced, generally resulting in a saturated gas at the elevated pressure. Due to the high cost of providing compression, it is used on its own only in limited applications. It is, however, used as the first stage with one of the other three methods. If a high-pressure gas is allowed to expand, the increase in volume and reduction in pressure result in a lower dew point. 

SENSIBLE HEATING COOLING is represented by a horizontal line between the limits of the process. All the properties of air change except the moisture content. 

This straight-line proportioning holds good to close limits of accuracy. The horizontal divisions of dry bulb temperature are almost evenly spaced, so indicating sensible heat. The vertical intervals of moisture content indicate latent heat. 

The refrigeration method of drying air is the most energy efficient, down to a lower limit of about 0.005 kg/ kg moisture content at atmospheric pressure. Equipment to work at frosting conditions can be duplicated, one evaporator defrosting while the other is operating. Below this limit, chemical or adsorption drying must be used [61]. 

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