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[Mill Management by D.J. Castillo, PhD]
dream steam
Better boiler maintenance for higher feed quality and economy
Steam is a key ingredient in almost all pelleted and extruded feed products. High quality feed requires high quality steam and most of this steam is produced in fire-tube and other types of boilers. Besides hydrothermal conditioning for pelleting and extrusion processes, steam often plays a role in cooking and drying ingredients and finished feed, cleaning fat from  equipment, and heating buildings and work spaces. However, for the feed plant to have a reliable source of high quality steam, the facility’s maintenance department must keep the boilers in optimum operating condition.
A well-planned boiler maintenance program not only avoids unnecessary downtime, it also promotes safety and aids boiler-code and local inspectors, according to Abilene, Texas-based Rentech Boiler System’s boiler maintenance experts. A plant’s boiler maintenance supervisor must establish a schedule of maintenance procedures and maintain a boiler room log, recording daily ,  weekly, monthly, and yearly maintenance activities. User-friendly computer now make this task easier and aid in determining the boiler’s “availability factor on shutdown frequency, economies, and length of service. However, automation dose not lessen the need for maintenance.
“with the advent of automatic controls, heating boilers are taken for granted even during the heating season,” says Brian Moore, PE, principal engineer and boiler specialist for Hartford Steam Boiler Inspection and Insurance Co, Hartford, Connecticut. But, the Rentech experts caution: “Even though the boiler has electrical and mechanical devices that make it automatic or semi-automatic in operation, these devices require systematic and periodic maintenance. Rather than relieving the operator from responsibility, automatic features free him or her from some repetitive chores, and provide time for upkeep and maintenance.”
Steam for multiple jobs
Scheduled maintenance can prevent unscheduled equipment down-time. However ,boiler maintenance in a feed mill or ingredient processing plant is complicated because the boiler may provide steam to several segments of the production line, performing a variety of roles from mash conditioning and cooking to product drying and space heating.
Rob Krawic, New England Mechanical Services Inc, Vernon, Connecticut, points out that most boilers have a burner that mixes air with a fossil fuel creating a fire that is sent into a combustion chamber and then through the remainder of the boiler’s tubes or passes. As the fire travels through this type of fire-tube boiler, the heat from the fire passes through the metal walls of the boiler into the water.
“The easier it is for the heat to travel into the water, the more efficient and less expensive the operation of your unit will be,” Mr Krawic points out. “Also, when the optimum adjustment of air-to-fuel ratio of each burner is achieved, it will allow you to save both energy and money.”

Air-to-fuel rattle
Adjustment of the air-to-fuel ratio is a critical feature in boiler maintenance. If not enough air is present, carbon monoxide gas may form, which can be lethal in confined spaces. If too much air enters the combustion chamber, the heat can exhaust from the boiler as it heats the water. Smoke, also produced during combustion, generates efficiency-robbing soot. One sign of soot buildup is an increase in stack temperature.
“One-eighth inch (3.2mm) of soot buildup ion the metal fireside walls of the boiler,” Mr Krawic says, “is equal to a 10% increase in fuel consumption.”
Regular boiler maintenance should include a number of key factors, including checking the boiler water lever in the gauge glass and the boiler steam pressure on the gauge, operating the intermittent blow-down valve to remove any accumulated solids in the mud drum, operating the valves on the water column and gauge glass to ensure that these connections are clear, and monitoring water chemistry to adjust the chemical feed treatment and continuous blow-down to keep the boiler within water-treatment guidelines. Rentech’s on-line boiler maintenance manual provides detailed boiler maintenance schedules (see box).
Early warnings
   Maintenance personnel need to be able to recognize unusual noises, improper gauge readings, leaks, and signs of overheating in order to begin corrective action to prevent unscheduled down-time or expensive repairs resulting from boiler failure. All piping connections to the boiler must be maintained in leak-proof condition because even a minor leak could soon become serious.
   “The applies especially to the water gauge especially to the water gauge glass, water level control, piping, valve packing, and man-way gaskets,” the Rentech experts emphasize. “If serious leaks occur, shut down the boiler immediately and gradually reduce steam pressure. Do not attempt to make repairs while the boiler is under pressure.”
   Hartford Steam Boiler’s Moore stresses the importance of monitoring water quality for optimum boiler operation: “If a heating system is leak-tight, water chemistry is usually not a major concern for cast iron boilers. Real world experience tells us, however, that leaks are all too frequent.
   “If a sufficient volume of raw water is added to a system, careful attention to water chemistry will help reduce scale and sludge accumulation. Sections can overheat due to lack of adequate water flow and heat transfer through the metal. Less dramatic, but just as effective in preventing proper operation of a boiler, are cracks from overheating.”
   Boiler using large amounts of make-up water with a high mineral content accelerate scale and sludge build-up. Softening the water reduces the mineral content, but can make it acidic which accelerates corrosion. Mr Moore cautions: “It is important to have raw water tested to determine if water treatment is required. If rusty water or sludge is visible in the gauge glass, you can bet that trouble is not far away.
Condensate sampling
   A mill’s boiler maintenance program should also include a steam condensate sampling plan. Before an operator should blow steam though the sample line to remove any material that may have been deposited and adjust the flow rate to the desired level during sampling. The condensate should flow at this rate for at least 1 hour before conductivity measurements are recorded or before a sample is collected for other methods of analysis, boiler maintenance experts say.
   When samples of condensate are collected for evaporative analysis, the flasks or other types of containers should be meticulously cleaned prior to use. Borosilicate glass is a satisfactory material for such containers but they should be aged by allowing them to stand for several days full of distilled water. This aging of borosilicate glass may be hastened by a preliminary treatment with dilute caustic soda (10 grams per liter). Containers fabricated from suitable metals or plastics may also be used.
   Samples should be analyzed as soon as possible after collection. After use, the flasks should be rinsed with hydrochloric aid. These flasks should be reserved and used for no other purpose than steam samples. When the condensed sample is to be analyzed by the electrical conductance method, cool it to 250C. When dissolved gases are to be determined, cool the sample to 200C or lower.
   If a boiler is an outside unit, has piping pr vessels in unheated spaced, or is shut down in cold weather, freezing may be a concern. Antifreeze can be used to help prevent freezing .Mr Moore says, “Most new boilers are being built with elastomer hydronic seals between sections however, these seals are susceptible to possible deterioration due to attack by petroleum-based antifreeze and water treatment chemicals.”
Blow-down technique
   Boiler operators conduct water blow-down to remove the concentrated water from the boiler’s pressure vessel. Blow-down is performed while the vessel is under pressure. The removed water containing suspended and dissolved solids is replaced with relatively pure feedwater. If a blow-down is performed, solids will become less soluble in the boiler water so that the water boils off as relatively pure steam. The remaining water becomes thicker with either suspended or dissolved solids, which contribute to scale and deposit formations. Boiler operators rely on two basic types of blow-down: Intermittent and continuous. Intermittent is done manually and is necessary for the operation of the boiler regardless of whether continuous blow-down is a continuous and automatic removal of concentrated boiler water.
   In a continuous blow-down, foaming may occur in the steam drum and cause large quantities of water to pass over into the steam lines. It can be detected by violent fluctuations or sudden dropping of the water level in the gauge glass. This trouble may be caused by dirt or in the oil in the boiler water, an overdose of treatment chemicals, carrying too high a water level in the steam drum, or excessive rates of change of evaporation. If the problem becomes serious, operators must decrease the load on the boiler, then alternately blow-down and feed fresh water several times. If foaming dose not stop, the boiler can be cooled , emptied, washed, and refilled with fresh, treated water. Boiler maintenance experts caution operators against experimenting with ‘home-made’ treatment chemicals.
   Good housekeeping helps to maintain a professional boiler room appearance and enhances boiler safety. The boiler room should be clear of all material and equipment not necessary for operation for the boiler, and only trained and authorized personnel should be permitted to operate, adjust, or repair the boiler and its related equipment. [FM]

Keeping boilers boiling
   Rentech Boiler Systems, Abilene, Texas, recommend the following maintenance schedule for conventional or fire-tube type boilers operating in production facilities, including feed mills:
Daily maintenance: Each day, boiler maintenance personnel should check the burner operation, including fuel pressure, atomizing-air or steam pressure, and the visual appearance of the burner. They should also clean the observation ports during periods of low fire or shutdown and test the boiler lever alarms and low-water cutoff.
Monthly maintenance: On a monthly basis, maintenance personnel must check the condition of the refractory for significant damage or cracking, and patch and repair the refractory if necessary. Frequent wash-coating of refractory surfaces is recommended with high temperature bonding, air-dry type mortar diluted with water to the consistency of light cream. This will seal small cracks and prolong the life of the refractory. Any large cracks should be cleaned out and filled with mortar.
Annual maintenance: A service technician from the boiler manufacture must inspect and check the entire boiler system annually. Also the heating and heated sides of the boiler should be cleaned. All man-way and hand-hole covers should be removed and inspected and bottom blow-down and drain valves should be opened and inspected. The maintenance personnel should wash the inside of the boiler with clean water under high pressure. A hand scraper can be used to remove accumulated sludge and scale, starting near the top and working toward the bottom. After cleaning tube exteriors, the tube surfaces should be checked for signs of overheating, such as bulging or blackened surfaces in the tubes.
On-going inspection: Boiler operators should follow the recommendations of their authorized inspector pertaining to safety-valve inspection and testing. The frequency of testing, either by the use of the lifting lever or by raising the steam pressure, should be based on the recommendation of your authorized inspector. Test the boiler safety valves in accordance with the manufacturer’s instructions to be certain that the valves are not corroded or do not open. Failure of the relief valves in an overpressure situation can be disastrous. [FM]

Boiler room at Southern States Cooperative’s Park City, Kentucky, plant with plant manager Gary, Huddleston (left) and American Feed Industry Association’s Keith Epperson. The Park City plant is always among the top contenders in the annual Feed Mill of the Year program and this year won the Most Improved Truck Fleet award.

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