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Article
A Steam Audit Can Help Your Facility
November 1, 2008 By: Steve Connor Paperboard PackagingSurging energy costs have facility engineers, managers and maintenance supervisors looking for ways to become more efficient in the plant. The most logical starting point for efficiency improvements: the boiler system.
 Keeping a boiler log monitors performance. |
The reason? Eight out of 10 boilers are more than 30 years old. They run less efficiently, are often unreliable and may even be in violation of federal standards on pollutant emissions. There are still 400 counties in the country that are considered U.S. Environmental Protection Agency (EPA) non-attainment zones, meaning they don't yet reach the current standards for air quality. The EPA is the highest-ranking regulator of boiler emissions, but many state and local governments are enforcing even stricter regulations.
One way to find out whether the boiler in your facility is efficient is to perform a steam audit — a comprehensive analysis of energy used within a facility, process or equipment, including recommendations for energy conservation measures.
Why do a Steam Audit?
Rising fuel costs are the number-one reason facilities do steam audits. Facility fuel bills can amount to between $1 and $3 million per year, eating up a large percentage of operating budgets.
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Those rising costs to the federal and state governments' push for energy efficiency, emissions reduction, and steam audit processes are becoming more popular at many facilities.
There are two types of steam audits: a simple boiler room audit and a complete facility audit. In a simple audit, a professional evaluates the boiler room including the boiler, and accessory support equipment, possibly extending the evaluation somewhat into the facility. With a complete site audit, auditors evaluate the boiler system as well as components throughout a facility, including steam traps, piping, valves, steam users, etc.
A simple boiler system audit costs approximately $1,000, whereas a complete site audit — depending on the number of steam traps and other equipment and the size of the plant — could cost a few thousand dollars.
The following detailed information is provided in an audit report:
- 1. Data acquisition: Identifies where and how a facility, process or equipment uses energy, along with costs and utility issues affecting the energy consumption.
- 2. Data analysis: Identifies energy conservation measures to make energy use more efficient, less expensive and more environmentally friendly.
- 3. Recommendations: A final report detailing what was found, a list of areas that need improvement and recommended actions, usually accompanied by some type of economic justification.
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About the Auditing Process
If your facility recently replaced the boiler system, more than likely a steam audit isn't needed. However, if the boiler system in the facility is more than five years old, a steam audit is highly recommended.
A steam audit can take several days to complete, depending on the type of audit and the size of the facility. A facility need not shut down for the procedure; it's actually better that the facility continues as usual so the auditor can easily spot steam leaks and other anomalies during daily operations.
During the boiler room audit, an auditor will check the boiler controls, the boiler, blow down, and feedwater conditioning to identify inefficiency issues. Auditors do an inventory of key equipment, looking for:
- 1. Energy-saving methods
- 2. Areas to implement better engineering practices
- 3. Health and safety concerns
During the complete facility audit, an inspector not only checks the inventory of key equipment in the boiler room, but also focuses on potential improvements throughout the energy using facility. The evaluator inspects the boiler, steam flow, pressures, temperatures, air handling, steam trapping, piping ancillaries including valving and insulation, condensate handling and heat recovery. Energy savings are sought through:
- 1. Identifying steam leaks
- 2. Heat recovery
- 3. Utilization of flash steam
- 4. Return of condensate
Top Findings in a Steam Audit: Damaged Boilers
One of the first things an auditor needs to determine is the condition of the current boiler system. The decision to replace a boiler shouldn't be based solely on the boiler's age. Some boilers, even 70 years old, remain in good condition. However, if the boiler is leaking, heavily scaled, or has outdated burners and controls, it's probably time to replace it.
If the boiler is in good shape, it may only need efficiency retrofits such as an updated burner or combustion control system, which can save 50 percent on capital costs compared to a whole new boiler unit and provide significant fuel savings at least equaling the retrofit cost the first year.
Auditors also investigate whether the boiler has been overheating. If the boiler overheats, there might be problems with either the boiler's insulation or gasketing, which could lead to damaged and unsafe equipment. The repairs to correct these types of problems are relatively nominal when compared to the consequences of letting the conditions exist resulting in serious safety or mechanical repair issues.
The auditor will perform a combustion test using "Stack Analysis Equipment" to see how efficient the facility's boiler is. This could lead to the recommendation that an oxygen sensor/transmitter in the exhaust gas is advisable.
The sensor/transmitter continuously senses oxygen content and provides a signal to the controller, which "trims" the air damper and/or gas valve, maintaining a consistent oxygen concentration. This minimizes excess air while optimizing the air-to-fuel ratio.
O2 trim systems typically increase efficiency by 1 to 2 percent, which if you're looking at energy bills in the millions means saving $10,000 or more.
How Is Steam Applied?
The next step in a steam auditing process is to determine what the steam is used for, how it's applied and if it is possible to reduce the operating pressure in order to save sensible heating requirements needed to produce a pound of steam.
To determine this, the heating process is reviewed along with the existing piping layout to see whether the diameter of the piping, controls, steam traps, and control valves can tolerate lower pressure, knowing velocities and pressure differentials will be changing.
If it is concluded the pressure can be reduced, fewer BTUs per hour will be needed in the process; therefore, saving the facility those energy dollars.
Stack Temperature
Stack temperature is also something to consider when looking for ways to be more efficient. A well-tuned boiler should operate between 50 to 100 degrees above saturated steam temperature. If a facility's boiler is operating at higher levels, fixing the problem begins with maintenance and/or cleaning.
From an efficiency standpoint, every 40 degrees in temperature reduction creates a 1 percent savings.
Sometimes, the stack temperature operates at higher levels because there is soot on the fireside surfaces caused by improper air/fuel ratio control meaning the burner was operating in a "rich" state causing fine black particles chiefly composed of carbon, to form on the heat transfer surfaces. This stymies heat transfer, causing considerable energy loss.
Soot can be mechanically cleaned with a flue brush. Once the soot is removed, a professional will need to recalibrate the burner. The return on your investment to reduce stack temperature is very quick, usually in less than one year.
Another cause of elevated stack temperature is scale formation on the waterside surfaces of the boiler caused by improper water treatment.
The remedy may be either acid cleaning or tube replacement dependent on the severity of the scaling condition. In either case, the fix, though more expensive than cleaning the fireside, is often paid back through energy savings in a year or less depending on boiler size.
Piping Conditions
In complete facility site audits, auditors survey the steam piping looking for energy losses through radiation and steam leaks; all identifiable to the naked eye.
Cutting down on steam loss through radiation is as simple as insulating the pipes and associated valving. Less than half of the process plant facilities surveyed have insulation on their piping or, the insulation applied is deteriorated to the point of uselessness. The larger the pipe diameter and greater the linear length, the more insulation can help in saving energy.
Reducing steam leaks caused by piping corrosion and compromised flanging can be another significant energy saver. The leaks appear as wisps of condensed steam, and once secured result in considerable dollars saved. See Table 1 above.
According to The U.S. Department of Energy (DOE), other opportunities to reduce energy costs with piping include ensuring steam mains are properly laid out, sized, drained and vented. An auditor can make sure that distribution system piping is sized to produce the appropriate system pressure drops; that it's adequately supported, guided, and anchored; and that appropriate allowances are made for pipe expansion at operating temperatures.
The DOE has an entire webpage devoted to helping companies become energy efficient at www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12530.
Feedwater System
During a complete facility audit, the auditor also will investigate how the feedwater supply to the boiler and condensate returns are being handled. Whether the water you're sending directly into your boiler is free of dissolved gases such as oxygen and carbon dioxide, which can be destructive to the boiler and condensate lines in the form of destructive corrosion.
To avoid these conditions, one thing an auditor may recommend is installing a deaerator for removing free oxygen and carbon dioxide from the boiler's feedwater.
Facilities should consider a deaerator if any of the following conditions exist:
- 1. Boiler plant operates at 75 psig or greater.
- 2. Boiler plant has limited standby capacity.
- 3. Production depends on continuous boiler operation.
- 4. Boiler plant uses 25 percent or more cold water makeup.
Auditors will also check to make sure the facility is using a water softener and that it's working properly. Without a water softener, scale will build up on the surface of the heat exchanger — and it doesn't take much scale to cause fuel usage to skyrocket; a 1/4 in. will increase fuel usage by 15 percent.
Auditors also examine condensate return. For many years, condensate was dumped down the drain. In the past few years, cost pressures and environmental concerns have forced facility engineers, managers and supervisors to rethink how they handle condensate.
Since condensate has already been through the steam system, it takes far less heat and fuel to turn it back into steam than it would to produce steam from an equal quantity of cold water. That's why steam users should return the condensate back to the boiler, where the whole process starts over again. This reuse can lead to hundreds of thousands of dollars in savings depending on the size of the boiler and its operating hours.
Feedwater Temperature
Facilities can also reduce their energy bills by taking a look at how much they spend on heating feedwater. An auditor will probably suggest an economizer, if your facility hasn't already invested in one, because an economizer can reduce the steam boiler's fuel requirements by transferring heat from the flue gas to incoming feedwater.
By recovering waste heat, an economizer can often reduce fuel requirements by 3 to 7 percent, and if you're looking at $1 million in annual energy costs — this retro can save you $30,000 to $70,000 a year.
To determine if an economizer should be used, the auditor considers the boiler size (200 HP or more is a likely candidate), the operating pressure of the boiler, the degree of burner modulation and the feedwater temperature. Given these considerations and knowing the hours of operation and fuel cost result in the ultimate payback.
Fuel
Fuel alternatives are also assessed during an audit, as adding another fuel burning capability may result in a lower primary fuel burning cost.
For example, by retrofitting a boiler's burner to burn to handle #2 oil, facility management can then negotiate with the local gas utility for a better rate because it can burn oil during peak gas usage times.
Steam Trap Audits=Health and Safety
Steam trap audits are typically performed during a complete facility site audit. Auditors look for traps, which are "blowing through," pressurizing the condensate line(s) causing water logging and inefficient process performance. Traps are normally checked using instrumentation employing heat sensitive or ultra-sonic sensing devices.
The other critical issue the auditor is looking for is evidence of water hammer.
In steam systems, water hammer most often occurs when some of the steam condenses into water in a horizontal section of the steam piping — usually caused by a poor condensation drainage strategy. Subsequently, steam picks up the water, forms a "slug" and hurls it at high velocity into a pipe elbow or other restrictive device, creating a loud hammering noise and greatly stressing the pipe.
Imagine a filled 8-in. pipe, 8-in. long. It weighs about 15 pounds or the same weight as a bowling ball. Now put 100 pounds of pressure behind the ball and it roll 60 miles per hour: that's the level of force when water hammer is occurring. It can cause pipes to break or even disintegrate if the pressure is high enough, potentially scalding or severely injuring employees in the vicinity. Clearly, it's a problem you'd want fixed.
If a steam trap audit is chosen, the auditor will:
- 1. Gather information on the number of steam traps in the facility.
- 2. Test and tag the steam traps.
- 3. Record findings.
- 4. Calculate energy saving measures and possible return on investment.
Maintaining a Boiler Log
To enhance the audit process and help keep boilers running optimally at all times, all facilities should keep a boiler room log.
A boiler room log sheet serves as a guide to a comprehensive maintenance program. The log sheet is used to evaluate performance and help spot trends that may affect operating pressure (steam boiler), operating temperature (hot water boiler) and stack temperature.
Boiler logs help you determine when to clean the boiler, adjust the combustion, repair or maintain the refractory or insulation and adjust water treatment, as well as replace safety devices, fuel filters or gaskets. Because the log keeps track of issues the boiler has had, the auditor will know what to look for up front.
For everyday safety, the log should also include a booklet of standard operating procedures, which serves as a "how-to" reference book for employees. Not knowing the proper procedures when an issue arises can lead to boiler outages and accidents.
The Return on Your Investments
The last key component of a steam audit is what you can expect in terms of return on investment for the suggested improvements and maintenance.
Facilities that invest in steam audits learn a lot about their boiler systems and why the energy bills may be going through the roof. Once a steam audit is complete, they also learn a lot about how they might proceed to conserve energy, reduce cost, increase reliability and improve safety.
Opportunities vary from simple cleaning procedures to replaced equipment and have paybacks that begin immediately — including keeping employees safe. By incorporating an auditor's energy efficiency suggestions, facilities may save hundreds of thousands over the next few years.
