How To Program An Air Washer

Transcription

1 AIR WASHER PROGRAMS THE BASIC SECTIONS OF AN AIR WASHER: The basic components of an air washer system are a chamber that contain a series of spray nozzles, an eliminator section that removes water from the air that is exiting the air washer and a sump which catches both the sprayed water droplets and the water that was collected by the eliminators. The spray section will either add moisture to the air or dehumidify the air, while washing solid particles out of the air. The eliminator section in many cases is a "W" or a series of "W"s in shape. This section, forces the air to contact the eliminator components, which in turn knocks down water droplets and air borne solids. The sump is the collection basin for the system. The washed out solids, lint, dust, and water all collect in this area. FUNCTIONS OF AN AIR WASHER: 1. Cool the air. 2. Humidify the air. 3. Dehumidify the air. 4. Clean the air of particles. 5. Hyperionize the air. HUMIDIFICATION BY AN AIR WASHER: Humidification is accomplished by using the recirculating spray water, washing preheated air with the spray water, and by heating the spray water. In general, the humidification of the air occurs as the humidity of the outside air decreases. This allows the water from the sprays to entrain in the low humidity air and increase the humidity of the washed air as it leaves the system for the plant. 1

2 Page 2 The heating of the spray water or the heating of the air prior to the air washer creates a condition that allows the air passing to the plant to hold a higher level of moisture. The amount of moisture that is required for the plant use will dictate the degree that the air or spray water will need to be heated. An air washer will humidify the air during the seasons when the outside air is low in humidity. This is usually during the late Fall, Winter and the early Summer, or in arid climates. The reason that the air is humidified, is to create the proper condition for the operation of the plant. In the production of Textiles, Electronics, and other related industries, where the humidity of the air is crucial for the air quality and material production, the air washer will balance the required humidity of the plant air by humidifying the air during the dry seasons, and dehumidifying the air when the air conditions are more humid than the plant requires. During the humidification process, the water in the air washer will cycle up solids in the same manner as a cooling tower. For this reason, the air washer is to be treated in basically the same manner as a cooling tower would be, that has the same water characteristics. The only differences in the chemical treatment program are based on the unique operating characteristics of an air washer, which are addressed in other sections of this report. DEHUMIDIFICATION BY AN AIR WASHER: Dehumidification occurs when the water that is spraying from the nozzles is cooler than the wet bulb temperatures of the incoming air. In this case, the incoming air is moist and contains a higher level of moisture than the plant requires. By spraying this air with colder water, the incoming air is cooled down. This cooling process also removes moisture from the incoming air. Dehumidification usually occurs during the hotter more humid months of the late Spring, Summer, and very early Autumn. During the period of time that the air washer acts as a dehumidifier, the air washer will take on the water that has been stripped from the air. This effect causes the dissolved solids level in the air washer to drop. It also creates a surplus of water in the air washer system that is removed from the air washer through the system overflow. As the solids level in an air washer drops, the Langelier Index will also drop. The index is used to indicate the tendency of the system water to be either scale forming or corrosive. During 2

3 Page 3 the period of time that the air washer acts as a Humidifier, the water in the system will tend to cycle up and establish a positive Langelier Index. This is scale forming and is treated as such. During the Dehumidification process, the water can become lower in solids and dissolved contaminants than the system make up water, this causes the water to have a lower Langelier Index and become corrosive. At this point, the chemical treatment program will need to be changed to protect the system from the potential corrosion that could occur at this time. The chemical treatment of an air washer must be looked at as two systems operating in one piece of equipment during different times of the year. CLEANING THE AIR WITH AN AIR WASHER: Air is cleaned by an air washer when particulate matter impinges on the wetted surfaces of the eliminator blades. Air is also cleaned, when the sprayed water generates enough ionization to neutralize the charges on the particles in the service area so that they can be dropped out into the sump as they are drawn through the air washer. The cleaning of the air will remove lint, oils, and other airborne particles from the air. This builds up the level of the solids in the water which must be removed either from over flow or bleed. Chemical treatment can improve particle removal and prevent nozzle clogging from excessive solids build up. AIR HYPERIONIZATION: As the water droplets are broken up at the nozzles, ionization occurs. This places a charge on the water droplet which allows it to attract charged particles that are in the air. This will allow the removal of any of the airborne solids from the air. It can also cause the build up of charges in the air that exits the air washer. These charges can cause static electricity to build in the air, which can cause textile processing problems if not neutralized by an antistat treatment program. RECOMMENDED AIR WASHER MAINTENANCE: Air washer systems should be inspected regularly to insure that wetted components are free of dirt, 3

4 scale, oil, debris, and microbiological fouling. Preventative maintenance and the use of chemical treatment programs, can virtually eliminate the problems that are caused by these contaminants, which reduce excessive man-hours for cleaning up the unit and down time. Page 4 BASIC COMPONENTS OF AN AIR WASHER TREATMENT PROGRAM: A good air washer treatment program should offer the following: 1. Even Humidity Control 2. Scale Control 3. Corrosion Control 4. Lint and Oil Vapor Control 5. Odor Control The proper application of chemical treatment products can allow your system to operate at its peak efficiency with minimum maintenance. HUMIDITY CONTROL FROM CHEMICAL TREATMENT: The proper use of dispersants and biological control agents allows the system water to remain cleaner. This improves the atomization at the nozzles which creates a finer droplet and a more uniform spray pattern. This is in part due to reduction in the surface tension of the water itself, coupled with the control and the removal of the potential system foulants. Because reduced surface tension allows the spray nozzles to break up water into a finer spray, the increased water surface thus exposed to the air stream promotes higher evaporation of the air stream. This finer spray pattern also assists the air washer in scrubbing the air more efficiently, which eliminates more airborne particles. The lower surface tension or "wetter" water also keeps the circulating system clean and prolongs operational time between clean-ups. AIR WASHER SCALE CONTROL: Scale is controlled in the air washer system by using a blend of dispersants and scale modifiers. These products distort the crystalline structure of the scale and as a result suspend the scale in the 4

5 water so that it can be removed through the bleed rather than allowing it to drop out on the system heat exchange surfaces. This improves the operation of the heat exchange potential of the system, maintains a cleaner spraynozzle and stops costly down time from scale build up. Page 5 The scaling potential for an air washer occurs during the time of year when the system is humidifying the air. Humidification allows the air washer to act similar to a cooling tower, where the water cycles up the solids in the water and eventually creates a scaling condition. At this time of year, the system can be treated very much like a cooling tower in both the areas of biological control and scale prevention. AIR WASHER CORROSION CONTROL: Corrosion in any metallic system is controlled by the passivation of the metallic surfaces that come into contact with the water. Carbon Dioxide, Sulfur Dioxide and other corrosive gasses scrubbed from the air stream can cause serious problems when dissolved in the water. They form dilute mild acids which will readily attack the unprotected metallic surfaces of the system. Nozzle loss is very characteristic of this condition. To correct this condition, we use corrosion inhibitors which lay down a thin monomolecular coating on the metal surface, while increasing the ph of the system to a level that is close to 9.0. This neutralizes the dilute acids, puts a protective coating on the metal surface, and retards the rapid growth of bacteria in the system. Corrosion is characteristic of conditions during the period when the air washer acts as a dehumidifier. At this point, the water that is washed from the air will dilute the natural buffers that are found in the water, and allow the ph of the system to slowly drop. The result is corrosion and the perfect conditions for bacteria growth. OIL AND LINT REMOVAL: Lubricating oils (oily smoke) that are atomized into the air steam due to heat generated from high speed machinery operations can foul the system. The build up of lint in the system will also cause system fouling. These problems can be controlled by using a oil emulsifier to pull the oil into the 5

6 water and then allow it to be removed with the bleed or overflow, and by low level foaming of the sump water. This foaming will float the lint and allow it to be removed with the bleed or the overflow. If left untreated, the oil in a system can film out and build up to a point that the system is forced to shut down. It can form jelly-like build ups on the eliminator sections of the air washer which will stop air and moisture flow. Page 6 INITIATION OF AN AIR WASHER PROGRAM: First the air washer must be cleaned thoroughly. This includes the removal of all solids and bacterial growth. Then drain and flush the system to remove solids from isolated areas. Then charge the system with the proper treatment products based on the time of year and atmospheric conditions. Finally, the system must be tested regularly to maintain the proper levels of products in the system during the different operating conditions. BIOLOGICAL CONTROL: An air washer puts air out for people to breath. As such, the air must be clean and free of odors. This eliminates many of the biocides as the sulfur based carbamates for use in this type of system. Air washers will build up a slime very rapidly. To control this the use of rapid oxidizers with low odor levels as bromine and hydrogen peroxide should be used in conjunction with a cationic or nonionic biocide. Usually this includes the use of one of the polyquat biocides or glutaraldehyde. The biocides should be fed twice each week in a shock type basis, with the oxidizers being fed continuously or as a shock weekly, based on the conditions of the system and the oxidizer being used. 6