|
|
|
The "MISTER" TECHNOLOGY The "MISTER" system consists of an arrangement of atomizing nozzles, whose function is controlled by a central control module. The control module maintains the required system operating pressure, filters the water supply, and activates the operation of the nozzles based on signals received from a sensor, which is specified according to the application. The "MISTER" system uses ordinary water which has been treated, filtered, and pumped up to between 600 and 1000 psi. It is then delivered down a ½" stainless steel tube or flexhose. Unique "MISTER" nozzles are placed at various distances along the tubing. These nozzles atomize the water into billions of micron sized particles which cool the surrounding air. The cooling effect created by the "MISTER" system is due to the "flash evaporation" of liquid H2O. This is the change that occurs when a liquid under pressure passes through a nozzle to a pressure low enough that some of the liquid vaporizes or flashes, producing a two phase stream of vapour and liquid in equilibrium. In the process of vaporizing, energy is consumed from the hot air, thereby reducing its temperature. "MISTER's" unique atomizing nozzles offer low flow rates as well as a high rate of forward discharge velocity. This results in high turbulence and therefore, extremely uniformed particle distribution. Each nozzle includes a non-corrosive stainless steel orifice and internal components. "MISTer" TECHNOLOGY A) TECHNOLOGY The "MISTER" system consists of an arrangement of atomizing nozzles, whose function is controlled by a central control module. The control module maintains the required system operating pressure, filters the water supply, and activates the operation of the nozzles based on signals received from a sensor, which is specified according to the application. The "MISTER" system uses ordinary water that has been treated, filtered, and pumped up to between 600 and 1000 psi. It is then delivered down a ½" stainless steel tube or flex hose. Unique "MISTER" nozzles are placed at various distances along the tubing. These nozzles atomize the water into billions of micron sized particles which cool the surrounding air, as well as increasing its relative humidity. B) CONTROL MODULE The two major components of the control module are a positive displacement pump and motor. Both of these are thermally protected by a dump valve that releases if the temperature exceeds 140 F. A pressure gauge and solenoid valves regulate both the inlet and outlet water flow. The inlet water must reach a pressure of 10 psi before the solenoid valve is opened. Likewise, the outlet water flow to the nozzles must reach a pressure of 100 psi before the solenoid opens. The pressure gauge has a six second delay feature. C) NOZZLES "MISTER" unique atomizing nozzles offer low flow rates as well as a high rate of forward discharge velocity. This results in high turbulence and therefore, extremely uniform particle distribution. Each nozzle includes a non-corrosive stainless steel orifice and internal components. A special O-ring seal design requires only finger tightening for a completely watertight seal. Nozzle orifice diameters range from 0.006" to 0.40", which corresponds to maximum flowrates ranging from 0.0121 to 0.1486 USGPM. These maximum flowrates are based on a 1000 psi operating pressure. Lowering the operating pressure of the system results in lower nozzle flowrates. Droplet sizes that were produced by different MEC nozzles were measured using Laser Doppler Anemometry by Aeromatics (Sunnyvale, California). Laser Doppler Anemometry (LDA) measures the scatter of laser-light from individual droplets to yield the size of the droplet as well as its velocity. The results showed that MEC's nozzles produced a broad spectrum of droplet sizes ranging from 1 to 50 microns. A majority the droplets, on a Sauter mean basis, were in the range of 20 to 40 microns in diameter. Also, it was known that nozzle size and operating pressure have only a minor effect upon droplet size distribution. D) NOZZLE LINE 1) Stainless Steel Type 304L stainless steel performs well under oxidizing conditions (e.g. acidic or alkaline solutions), since resistance depends on an oxide film on the surface of the alloy. It is easily fabricated into complex shapes and can withstand temperatures up to 1500 F. 2) Flexhose MEC Systems Inc. uses a ¼" diameter flex hose for specific applications where stainless steel would be impractical. E) WATER SUPPLY In all atomization systems, one must pay close attention to supply water quality. MEC's nozzle designs include very small diameter orifices and very narrow passages. Water with Total Dissolved Solids (TDS) counts exceeding 300 PPM or with high calcium of pH levels should be treated in order to prevent excessive nozzle blockages and/or excessive filter cartridge maintenance. If the water quality is in question, a water analysis report should be obtained. The "MISTER" system is provided with four stages of water filtration: 30 microns, 10 microns, 5 microns, and 1 micron. This will aid in the prevention of nozzle plugging. BASIC FUNDAMENTALS A) VAPORIZATION The conversion of a liquid to its vapor is called vaporization. Heat must be absorbed by the liquid for this process to occur. For instance, in order for 1 mol (18 g) of liquid water to be completely vaporized at 20 C, 44.10 KJ (41.80 BTU) of heat energy must be absorbed. The amount of heat required to convert one mole of liquid into one mole of vapor at a given temperature and constant pressure is called the latent heat of vaporization. H2O (1) +44.1 KJ H20(g) It always requires heat to vaporize a liquid because of the greater magnitude of the force of attraction between the molecules in the liquid state as compared to the gaseous state. Energy must be supplied to overcome the force of attraction between molecules in the liquid, to pull them apart and increase the distance between the molecules. The energy supplied increases the potential energy of the molecules.
The cooling effect created by the "MISTER" system is due to the flash evaporation of liquid H20. This is the change that occurs when a liquid under pressure passes through a nozzle to a pressure low enough that some of the liquid vaporizes or "flashes", producing a two phase stream of vapor and liquid in equilibrium. Water is first filtered, and then pumped to as much as 1000 psi. The water is then sent to "MISTER" unique atomizing nozzles. When the water passes through these nozzles, flash evaporation occurs. The energy required for this vaporization to occur is provided from the surrounding air in the form of heat, thus cooling the surrounding air. C) IMPACT The impact of
MEC's high pressure spray is given by the following formula: The variables affecting the impact of a spray are flow rate, spray angle, concentration of the spray, operating pressure, and air friction. These variables will either affect the mass per unit time or the velocity and this affects impact. The flow rate is, of course, essentially the mass per unit time. The drop sizes affect the velocity in that smaller drops lose velocity due to air friction more rapidly than the larger ones.
A) PARTICULATE EMISSIONS Particulates may be defined as solid or liquid matter whose effective diameter is larger than a molecule but smaller than approximately 100 m. Particulates dispersed in a gaseous medium are collectively termed an aerosol. Particular types of aerosols include: dust, smoke, fog, and haze. The adverse health effects of particulates depend not only on their amounts but also on their chemical and physical properties. Particle size limits access to the lungs. Those reaching the lungs by mouth are usually less than 15 m and by nose, less than 10 m. Fine aerosol particles, 2 m or smaller, ultimately reach the lung's fine structures, the individual alveoli. The effects produced depend on chemical properties such as toxicity, acidity, and solubility. The "MISTER" system removes particles from gas by capturing the particles in water droplets and separating the droplets from the gas stream. The droplets act as conveyors of the particulate out of the gas stream. The three main mechanisms utilized in capturing particulates include: I) Inertial Interception On approaching a collecting body, a particle carried along by a gas stream tends to follow the stream but may strike the obstruction because of its inertia. ii) Brownian Diffusion Smaller particles, particularly those below about 0.3 m in diameter, exhibit considerable Brownian movement and do not move uniformly along the gas streamline. These particles diffuse from the gas to the surface of the collecting body and are collected. iii) Flow-line Interception If a fluid streamline passes within one particle radius of the collecting body, a particle travelling along the streamline will tough the body and may be collected without the influence of inertia or Brownian diffusion. These mechanisms cause the tiny pollutant particles to be lodged inside the collecting droplet. The larger droplet is then separated from the gas stream by gravity. Because of the minute size of fog droplets produced, the "MISTER" system is best suited for the elimination of very fine particulates. B) FUGITIVE DUST Dust is typically formed by pulverization or the mechanical disintegration of solid matter into particles of smaller size by processes such as grinding, crushing, and drilling. Particle sizes of dust range from a lower limit of about 1 micron up to 100 microns and larger. Dust particles are usually irregular in shape and will not flocculate or settle under the influence of gravity. Common examples incluse fly-ash, rock dust, and ordinary flour. Dust collection is concerned with the removal of these particles for the purpose of: 1) Air-pollution
reduction It is well known that increasing the relative humidity of air will significantly reduce the amount of dust in the air. The "MISTER" system controls low humidity levels in the air, thereby reducing this problem.
Smoke implies a certain degree of optical density and is typically derived from the burning of organic materials such as wood, coal, and tobacco. Smoke particles are very fine, ranging in size from less than 0.01 m to 1 m. They are usually spherical in shape if of liquid or tarry composition and irregular in shape if of solid composition. Owing to their very small particle size, smokes can remain in suspension for long periods of time and exhibit lively Brownian motion. Convection flow causes reburn. FORESTRY INDUSTRY A) Hygroscopic Materials Hygroscopic materials are defined as those which are able to take on or give up moisture, thereby changing their regain. They are particularly sensitive to humidity changes in their environment. When these materials finally reach a balance, where they are stable and no longer take on or give off moisture, they are said to have reached their equilibrium moisture content (EMC). When a hygroscopic material is stabilized at its EMC for a particular temperature and relative humidity, there is little effect on the material. The problems begin when the relative humidity begins to drop and the air pulls moisture from the material, upsetting its EMC. When the material loses moisture it will shrink, warp, crack, and become thirsty for solvents. This causes problems not only with the material, but also with the machinery, finishing processes, coatings, etc. Weight and texture are also significantly effected. When the EMC is upset to the point of damaging a product and rendering it unsalable, economic loss results. This includes the loss of any and all energy required to manufacture that product, and the additional energy input and labour expense if the product is reworked.
Wood is a hygroscopic material, able to take on or give up moisture to the surrounding air. As wood takes on moisture it swells, as it gives up moisture it shrinks. The amount of moisture in the wood, expressed as a percentage of it's dry weight, is referred to as its regain. Regain will vary with temperature, relative humidity, and type of material. As wood loses moisture it shrinks, however, the tangential shrinkage is much greater than radial shrinkage. This causes dimensional changes and instability in the wood and it will pull apart along the grain, causing cracks. If the wood is strong enough not to crack, it will warp as the uneven shrinkage occurs. This is why it is important to condition wood to the proper regain for best workability and then stabilize it at the corresponding EMC by maintaining proper humidity control. Optimum conditions for wood constitute a regain between 5% - 9%, depending on the wood and its use. This corresponds to the EMC with 35% - 45% relative humidity air at 75 F.
The "MISTER" system is ideal for use in lumber dry kilns. It can be used with lumber of any species and thickness and can be installed in both conventional and dehumidification dry kilns. The "MISTER" system provides solutions to many problems experienced during conditioning and equalization. First, it eliminates the tendency of the dry bulb temperature to rise uncontrollably. This rise in temperature decreases the relative humidity in the kiln, reduces the effectiveness of the conditioning process, and lengthens the time required for equalization/conditioning. This temperature rise is due largely to an enthalpy decrease when high-temperature, high-pressure steam is released into the kiln interior. A smaller heating effect results from the temperature change undergone by the steam as it leaves the spray line. It is estimated that the combined effect of these two factors result in a release of 1,270 BTU each for pound of water vapor absorbed into the lumber. If a cool water spray were to be used in place of live steam, approximately 1,112 BTU/lb of spray would be used in raising the temperature of the water droplets to the kiln interior temperature. This would largely offset the 1,270 BTU/lb released when the vapor entered the wood surfaces, thereby significantly reducing the heat problem. Another advantage of using the "MISTER" high pressure system with conventional kilns is the steam savings. Take the case of a mill with several kilns which are heated by a waste wood boiler. When the mill was constructed, the boiler was oversized to allow for future kilns. As these were added, the excess heat capacity of the boiler decreased to the point that the output of the boiler would not support additional kilns. By replacing the steam spray systems in all kiln attached to the boiler with the "MISTER" system, enough energy can be saved to permit the construction of additional kilns without an expensive boiler upgrade.
|
|
© 2003 MEC Systems
Inc. |