Gas Technology: Industrial humidification solutions

Holding the ideal level

By Plant Engineering December 20, 2011

In our homes we recognize when humidity levels are too low. We may have respiration problems, dry or cracked skin, and have those annoying static electricity snaps as we touch household objects. In older times, we tried to overcome those problems by putting a pot of water on the stove. Today, we use humidifiers and vaporizers to increase room humidity. We encounter the same issues in the workplace, sometimes with more serious consequences. There are solutions.

A sweet spot for humidity

In most of North America there is an annual outdoor natural humidity cycle. Humidity levels are high, often excessive in the warm months, and low in the cold months. Indoors, these levels tend to be exaggerated by cooling in the summer and especially by heating in the winter. In the northern U.S. and much of Canada, winter humidity levels as low as10-20% are not unusual. Purely for human comfort, expert recommendations range from 30% to 50%.

For large commercial and industrial buildings, the annual humidity cycle also prevails. Humidification requirements, however, may vary. It depends on the type of building and the sensitivity of different products and processes. Matt Nowak is North American Sales Manager for the Humidification Group of Armstrong International, a major supplier of large humidification systems. He explains possible solutions.

Comfort and product protection

Nowak indicates that humidification systems are installed in industrial and warehouse facilities for a variety of reasons. “The majority can be summed up in three areas of concern: electrostatic discharge (ESD), hygroscopic material protection, and health and human comfort.” Nowak says that Armstrong International provides many types of units for differing applications, including various supply water qualities, as well as multiple humidifier control system types. “This includes the ability to be controlled via a building automation system (BAS).”

Eliminating ESD is important not only for worker comfort and safety, but also to protect settings and calibration on electronic devices including process controls. Hygroscopic materials including wood, paper and leather require higher ambient humidity levels to assure dimensional stability and product quality. Printing operations and paper storage require especially tight controls on humidity to prevent paper from shrinking, curling or jamming in processing equipment.

Supplementary humidification needed

For these facilities, optimum relative humidity levels may be as high as 60%. For certain applications, adiabatic humidifiers use a fogging unit to discharge a stream of 100% saturated air areas needing exceptionally high humidity levels. Such an area might be in the proximity of a printing press or other paper handling equipment.

Nowak notes that gas-fired humidifiers are sometimes compared to electric units. He notes, “The gas units offer two specific advantages; they typically have almost double the maximum output, and the required energy cost is less.” He indicates that the trend in industry is toward energy conservation and sustainability. “With these concerns in mind, in industrial markets the types with the most potential are gas-fired and adiabatic humidifiers.”

Armstrong International offers its gas-fired HumidiClean package humidifier for this market. Armstrong claims that this unit has an annual operating cost of about $2,700 compared with $5,000 for an electric unit. It features a low NOx burner and has an operating energy efficiency of 82%. It is available in a range of sizes for different building conditions.

Scale management important

Seldom are humidifiers supplied with 100% distilled water, so management of scale from minerals in the water is important. Armstrong uses ionic bed technology in the HumidiClean to reduce mineral buildup on the heat exchanger and sides of the tank. Nowak explains, “The scale is actually attracted to bed inserts when the water approaches boiling. This allows the steam generator to operate for longer periods of time without drain cycles to flush mineral deposits, saving energy due to less wasted hot water.”

The ionic beds consist of a fibrous medium that attracts solids from the water as its temperature rises, minimizing buildup of solids on the heat exchanger and inner tank walls. When the ionic beds reach their capacity of solids, a signal light indicates that it is time to change them. A new ionic bed weighs approximately 0.75 lbs. When it reaches its capacity, the bed may weigh more than 4 lbs. Use of this technology means reduced cleaning of the tank heat exchanger and reduced water and energy consumption through fewer required tank blowdowns.

Steam humidification

Another approach to humidification in plants that have steam boilers is direct steam injection into the air stream. According to Paul Pack, Process Steam Sales Manager from Fulton Boiler Works, many industrial and commercial humidification systems use this concept. He explains, “Longevity, low maintenance, precise control and rapid response to control signals are some of the distinct advantages of direct injection systems.” He notes that correctly conditioned steam acts as a system cleaning agent to keep the humidifier components free of mineral deposits that are typical with other forms of humidification.

Use the right boiler

According to Pack, not all boilers are suitable for this application. “Because steam humidification systems require large amounts of make-up water, the boiler system above all other considerations must be a forgiving piece of equipment. Boilers with small diameter water tubes, thin-wall boiler tubes, low water volume, poor steam quality or high heat release are generally not suitable for these applications.” He notes that the best boilers are rugged in design with a record of performance in an abusive system.

Pack points out that the boiler steam nozzle and steam piping must be properly sized to allow the highest quality of saturated steam possible. The system should account for the make-up water oxygen and mineral content without the use of boiler chemicals. The make-up water should be softened or demineralized, and the use of a tray-type deaerator rather than a standard spray deaerator is recommended.

Advantages of direct injection

Pack indicates that steam injection systems can be easily applied in tight spaces without causing wetting of the air ducts. He says, “As the steam is entirely a vapor, it only needs to be mixed with the air stream to satisfy the system humidification requirements.”

Humidification in typical industrial and commercial buildings is controlled by the building automation system. Pack explains, “In addition to the system’s DDC processor, the three main components of the control system are the air flow sensor, room humidity sensor and duct high level humidistat. The air flow sensor is located in the supply air duct and will shut down the humidifier to prevent water damage if the air flow is interrupted for any reason.

A high limit humidistat is located downstream of the steam dispersion tube and will shut down the system if the relative humidity is excessive.” He indicates that large spaces, critical function areas such as museums, or areas with high make-up air requirements may have multiple sensors.

Boiler industry offers help

Fulton and other steam system suppliers offer injection humidifier packages that are compatible with their systems, and can provide additional information on necessary make-up water treatment and humidification system controls. Humidifier systems can be included in new construction packages, or can be retrofitted to existing installations.

Especially with direct steam injection systems, it is important that the owner get expert help in determining whether the existing boiler and water supply is suitable. If your plant atmosphere is excessively dry during parts of the year, humidification is the answer, and natural gas-fired solutions are often the best choice.