With the goals of reliability and long equipment life in mind, there are a number of factors to evaluate when designing an industrial steam process system. The following tips will help ensure that you get the most from your system. However, remember to consider local jurisdictional installation requirements as well.
01 Think Gross, Not Net
When selecting the boiler for an application, key factors include the available fuel, floor space and clearances, required operating pressure, and NOX emissions
Always size the boiler for the gross load, not net load. The difference between gross and net is the heat loss from the process piping distribution system.
Always size the boiler for the gross load, not net load. The difference between gross and net is the heat loss from the process piping distribution system. On a large industrial heating system or heating load, this loss can be as great as 31 percent. If the boilers are sized for the net load only, the steam will condense as quickly as it is being utilized and never develop a head of steam.
02 Facilitate Peak Burner Performance
Check the amount of combustion air that is available to the burner. The burner must have enough air to fire at peak performance. An exhaust fan or similar equipment can create down draft in the stack or restrict the burner’s air supply, which will result in poor combustion. It is essential that only fresh air be allowed to enter the combustion air system. Foreign substances in the combustion system can create hazardous conditions.
03 Consider Steam Velocity
When designing the steam piping, consider the velocity of the steam and the outlet of the boiler. The velocity should be kept as low as possible to minimize the possibility of bouncing water levels and frequent low water cutouts. This also will allow a margin of error for upset boiler water chemistry conditions with a high boiler water total dissolved solids level.
04 Comply with ASME Piping Code
The current ASME section I code dictates that the near-boiler piping be installed per ASME requirements for Boiler External Piping (BEP). The piping must be hydrostatically tested and documented as indicated by this code section. (In addition, any local jurisdictional requirements must be satisfied.) One way the hydrostatic testing and documentation can be accomplished is by having the boiler equipment manufacturer install the boiler steam trim piping, low water cutouts, surface blowdown piping, and bottom blowdown piping at the factory. The boiler manufacturer would perform hydrostatic testing prior to shipment and complete the appropriate ASME documentation.
05 Correct Connections
If connecting two or more boilers to a common steam header, ensure the connection from each boiler (with a manhole opening) has two stop valves, and a sufficient free-blow drain exists between boilers. This also is important when a single boiler is connected to a header with a secondary steam source.
06 Understand Pressure Ratings
Be aware of flange and fitting pressure ratings. The ratings and certification information are stamped on the circumference of the flange. A 150-lb flange indicates a pressure temperature rating. This is not the maximum allowable working pressure (MAWP) of the flange; instead, it is a designation that allows a certain pressure use based upon the installation and temperature to be encountered. The pressure and temperature ratings can be found in ASTM A 105 B 16.5 specification tables.
07 Check Your Check Valve Size
Never size the boiler steam supply stop/check valve based on the steam supply line size. The steam stop/check valve must be sized for the valve to have a pressure drop at the average boiler steam flow and operating pressure. If the stop check valve is oversized, the valve sets will chatter during normal operation and will not seal after a few months of use.
08 Install Steam Traps
A steam trap should be installed at every low point in the system where condensate can collect. The piping should be pitched in the direction of the steam flow to ensure that the condensate will not travel against the flow in order to reach a trap. The critical steam traps in locations such as the steam header should have a valved bypass around the trap to enable the operator to test and drain the devices on a periodic basis.
09 Insulate Piping
All steam and condensate pipes should be properly insulated. Insufficient or damaged pipe insulation will cause excessive and costly heat loss along with possible condensate buildup, which could result in pipe failure. Valves and fittings have relatively large surface areas from which heat radiates. Insulating valves and fittings, as well as the piping, will provide energy savings and protection from burns.
10 Think About Pump Flow
Base the discharge pressure of feed water pumps on ASME requirements, in addition to the pressure drop in the piping and valves between the pump and the boiler. Safety considerations for the pump flow rate include the type of feed water control (on/off vs. modulating), and the boiler design. Modulating the feed water offers higher operational efficiencies for your system.
11 Gain Control
All modern steam process boilers should be controlled correctly to ensure that they are being operated at their peak efficiency and firing rate. This can be accomplished through the installation of a modern control system based on direct digital control (DDC), properly programmed for the installed system and load. Not only will the system reduce energy consumption, but it also will allow for the monitoring and trending of operational data. Effectively controlling boiler operation to match steam load requirements decreases boiler cycling and reduces maintenance costs.
12 Maintain Water Chemistry
Water chemistry must be maintained per the boiler manufacturer’s recommendations. Water chemistry should be sampled in both the feed water and the boiler water. Water softeners, carbon filters and chemical feed systems may be incorporated to achieve the proper chemistry. Other considerations include conductivity based on timed surface blowdown, and automatic bottom blowdown to control levels of total dissolved solids.
13 Maintain Your Equipment
With the high cost of fuel and unexpected plant shutdowns, a yearly preventive maintenance plan with a boiler combustion analysis is highly recommended. The yearly preventive maintenance plan should include checking all boiler safeties for proper operation.
Even the best designed system will provide less than optimal results if system maintenance is ignored. Poorly designed systems will struggle to provide adequate steam and can even present a hazard. Work with a reputable system designer to ensure safe and effective steam heating.
Paul Pack is an industrial steam process sales manager and Melissa Wadkinson, P.E., is a chief engineer at the Fulton Companies, Pulaski, N.Y., a manufacturer of boilers, thermal fluid heaters and temperature control systems. To learn more from Fulton, call (315) 298-5121 or visit www.fulton.com.