Humidifier

Humidification. For wiater operation, or for special process requirements, humidification maybe required (see Simultaneous HEAT and mass transfer). Humidification can be effected by an air washer which employs direct water sprays (see Evaporation). Regulation is maintained by cycling the water sprays or by temperature control of the air or water. Where a large humidification capacity is required, an ejector which direcdy mixes air and water in a no22le may be employed. Steam may be used to power the no22le. Live low pressure steam can also be released directly into the air stream. Capillary-type humidifiers employ wetted porous media to provide extended air and water contact. Pan-type humidifiers are employed where the required capacity is small. A water filled pan is located on one side of the air duct. The water is heated electrically or by steam. The use of steam, however, necessitates additional boiler feed water treatment and may add odors to the air stream. Direct use of steam for humidification also requires careful attention to indoor air quahty. 

Another method of moderate dehumidification is by direct contact between the air and cold water using open circuit equipment. An air washer or capillary humidifier maintaining the water at a cold temperature is an example. 

Avoiding sick building syndrome requires special consideration of building constmction and maintenance material used. Asbestos, organic solvents, paint sprays, dirty filters, moist environment caused by poorly maintained humidifiers, and dirty HVAC machinery have contributed to the deterioration of indoor air quahty. Nonstop quahty maintenance is required at all times. 

Another concentration method involves passing an inert gas such as N2 or CO2 through the reaction medium (12). As the gas passes through, it becomes humidified and carries captured water with it. Most of the energy required for the gas humidification comes from the heat of reaction. An advantage is that expensive drying equipment is not needed. Also, the sulfuric acid mist formed in typical concentrators is minimized. Du Pont uses a similar process in its nitrobenzene production faciUty. 

Acid cleaners based on sulfamic acid are used in a large variety of appHcations, eg, air-conditioning systems marine equipment, including salt water stills wells (water, oil, and gas) household equipment, eg, copper-ware, steam irons, humidifiers, dishwashers, toilet bowls, and brick and other masonry tartar removal of false teeth (50) dairy equipment, eg, pasteurizers, evaporators, preheaters, and storage tanks industrial boilers, condensers, heat exchangers, and preheaters food-processing equipment brewery equipment (see Beer) sugar evaporators and paper-mill equipment (see also Evaporation Metal surface treati nts Pulp). 

Figure 11-69 describes a typical central system. Either water or direct-expansion refrigerant coils or air washers may be used for cooling. Steam or hot-water coils are available for heating. Humidification may be provided by target-type water nozzles, pan humidifiers, air washers, or sprayed coils. Air cleaning is usually provided by cleanable or throwaway filters. Central-station air-conditioning units in capacities up to about 50,000 cu ft/min are available in prefabricated units. 

Evaporation of medium provides a little cooling. The inlet air to particulate filters must not be near saturation because condensation of moisture on the filter medium mobihzes contaminating microorganisms so that their chances of penetration are greatly increased. Sometimes humidified air is used, and the filter unit is heated to prevent condensation. However, this is common only for small equipment where the extra operations are relatively easy to install and maintain. 

Zinc Roasting Sintering Calcining Retorts electric arc Particulates (dust) and SO2 Particulates (dust) and SO2 Zinc oxide fume, particulates, SO2, CO Exhaust system, humidifier, cyclone, scrubber, electrostatic precipitator, and acid plant Exhaust system, humidifier, electrostatic precipitator, and acid plant Exhaust system, baghouse, scrubber or acid plant... 

Pretreatment of the raw waste gas to remove particulates, adjust temperature and humidify to saturation. 

Diy systems, where the gas stream is humidified and chemicals are added to the system... 

To control the humidity in a conditioned space humidifiers and reheaters are provided in AHU. Humidifiers to increase and reheaters to decrease the humidity. 

Injection of humidified and heated compressed air—Compressed air from a separate compressor is heated and humidified to about 60% relative humidity by the use of an HRSG and then injected into the compressor discharge. 

A commercial combustion turbine with the provision to inject, at any point upstream of the combustor, the externally supplied humidified and preheated supplementary compressed air. Engineering and mechanical aspects of the air injection for the compressed air injection plant concepts are similar to the steam injection for the power augmentation, which has accumulated significant operating experience. 

Figure 2-41. Heated and humidified eompressed air injeetion system for power augmentation of a gas turbine.

The analysis of the different cycles examined here, which range from the simplest cycle such as evaporative cooling to the more complex cycles such as the humidified and heated compressed air cycle, are rated to their effectiveness and to their cost is shown in Table 2-1. The cycles examined here have been used in actual operation of major power plants, thus there are no cycles evaluated that are only conceptual in nature. The results show addition from 3-21% in power and the increase in efficiency from 0.4-24%... 

The concept of injecting humidified and heated compressed air just after the gas turbine compressor is another very interesting way to increase power and efficiency. In this system, compressed air is added to the compressed discharge air. The compressed air is about 5% of the main gas turbine air and this air after it has been compressed using an external compressor is then injected into an air saturation device where steam obtained from the HRSG unit is then injected into the device to saturate the air with water and the saturated air then is further heated in the HRSG before it is injected into the compressor discharge of the gas turbine. 

Humidified Compressed Air Injeetion System are about the same. This is due to the faet that though the initial eost to install the Compressed Air System, for a turbine of about 100 MW, is about 3.7 million as compared to about 1.7 million for a steam injection system, the power generated by the Heated and Humidified Compressed Air Injection System is much higher. 

Injection Pre.s.sure. The injeetion pressure must be between 75-100 psia (5-7 Bar) above the Compressor Diseharge Pressure. In the ease of the Heated and Humidified Compressed Air injeeted system, the air must be saturated. 

Nozzle Area of the First Turbine Stage Expander Stage). This is a very eritieal parameter and limits the total airflow into the turbine seetion, thus this limits the amount of steam injeetion or the amount of the heated and humidified eompressed air injeetion. 

NOx Emissions. The amount NO emissions is very eritieal in most regions where gas turbines are being utilized for power generation. The present eap is about 22 ppm the aim is to go down to as low as 9 ppm. The teehniques offered here all are NOx emission friendly, in that they do not inerease the present levels of NOx, in faet in the ease of the injeetion systems, both steam, and heated and humidified eompressed air will lower the NOx emissions making the plant even more environmentally friendly, espeeially in this eritieal loea-tion. 

Control Systems. The eosts in all these systems have taken into aeeount modifieations of the eontrol systems. The eontrol systems in most of these eases will have to be new to take into aeeount the injeetion of steam, and the heated and humidified eompressed air, the HRSG, and all its assoeiated equipments sueh as pumps. 

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