Are you a factory owner? Looking for a way to lower your operating cost? Among all of the options you may consider, reduction of energy uses without decreasing productivity is the most efficient way. Energy audit has become a growing interest in recent years due to its direct impact in production cost. Energy audit is the first step to assess how much energy an organization consumes and what measures the management can take to make the organization more energy efficient. It will save significant amounts of money over time.
Almost all of the industrial facilities use boilers for heating water or producing steam. In facilities that use boilers, a large percentage of the energy/fuel consumption is accounted for by the boiler plant. As such, significant energy can be saved by optimizing boiler systems. This article describes some energy saving strategies of boilers system. Measures to improve your boiler efficiency will not only lower your production cost but also reduce greenhouse gas emissions and help you to contribute to promote cleaner environment.
Some strategic improvement options may include:
- Excess air reduction: A typical combustion process in boiler involves burning of fuel in presence of oxygen to produce heat. Air is used as a source of oxygen. To unsure complete combustion, excess air is provided than required. Since excess air reduces boiler efficiency by removing heat, the objective is to ensure that optimum amount of excess air is used. Usually 10 to 15% of excess air than stoichiometric ratio is provided for complete combustion. For boilers operating at high excess-air levels, the combustion burner operation needs to be tuned to adjust the air-to-fuel ratio. This can normally be achieved by adjusting the mechanical linkages that control fuel and air flow to the burner to provide the correct ratio between the two at different operating loads for the boiler. Ideally, an oxygen (O2) trim system should be installed, which can continuously monitor the oxygen level in the flue gas and automatically adjust the air-to-fuel ratio to maximize combustion efficiency.
- Burner and control upgrades: Some old burners may require more excess air than others. This boiler can be replaced with low excess air burner to improve efficiency.
- Variable speed drives on combustion air flow: variable frequency/speed drives or VFDs are can be used to control air flow. This can reduce electricity energy consumption than fixed drive fan and save money.
- Fuel switching: Many modern boilers are duel fuel type. The fuel cost may vary based on seasons or due to other reasons. A particular fuel may not be most economical at all times. So, switching between fuel based on cost can help reduce cost.
- Optimizing pressure system: Boiler has a maximum operating pressure rating based on their construction, as well as a minimum value to prevent carryover of water. Since boiler efficiency depends on operating pressure, where operating pressure is very high, it can reduced to actual requirements to save energy. In addition to improve efficiency, reducing steam pressure will help to reduce steam leaks.
- VFDs on feed water pump: in larger system, multiple boilers can be served by a common feed water pump. In this system, individual boiler take the required water by opening the feed water valve and excess water is returned back to the feed water tank. This results in wastage in electrical energy. This system can be improved to reduce the energy by using VFD pumps which helps maintain a set pressure in the feed water header pipe.
- Minimizing conduction and radiation losses: Boiler, auxiliary equipment and steam distribution piping system are much hotter than surrounding areas. So they lose heat by radiation and conduction. To minimize heat loss, all hot surfaces should be insulated with proper material and insulation should be of adequate thickness and in good condition.
- Heat recovery from the flue gas: Since the temperature of the flue gas leaving a boiler typically ranges from 150 to 2500C, heat can be recovered from the flue gas by passing it through a heat exchanger (economizer). Recovered heat can be used to preheat boiler feed water, combustion air or in other applications in the facility.
- Automatic boiler blowdown and heat recovery: Make up water used in boiler contains various impurities. When water is converted to steam, the concentration of impurities that remain in the boiler increases. This impurities may lead to accelerated corrosion, scaling and fouling. So, boiler blowdown is necessary where concentrated water is removed at steam temperature periodically or continuous and fresh water is entered in the boiler to maintain a certain level. Energy losses can be minimized if automatic blowdown is installed and heat from blowdown can be recovered. In automatic system, it monitors the pH and conductivity blowdown happens only when required to maintain acceptable quality of water. Heat can be recovered from blowdown by installing a heat exchanger to preheat the boiler feed water.
- Condensate recovery: The condensate in steam system contains a significant amount of heat energy. If the condensate is returned to the boiler feed water tank, it will result in significant heat energy savings. Recovered condensate will help to reduce water consumption, water treatment cost and blowdown.
- Steam traps: Steam traps are used in steam systems to remove condensate and noncondensable gases. Over time, internal parts of steam traps wear out and result in failure to open and close properly. While an open trap would result in loss of live steam, a closed trap could result in loss of heat transfer area and water hammering. Water hammering can eventually result in damage to valves and other components in steam systems, which could result in steam leaks. So, traps should be periodically inspected and repaired or replaced to ensure that they are in good working condition. In addition, the correct type of steam trap should be selected for each application
- Steam leaks: Steam leaks can be found in pipes, flanges, valves, fittings, connections, traps and in other process equipment. If all of the leaks can be eliminated, substantial amount of money can be saved from steam distribution system.
- Cleaning of heat transfer surfaces: Fouling, scaling and soot build up on heat transfer surfaces of boilers act as insulator and may lead to reduced heat transfer. Typically, 1-1.5 mm soot build up in the fire side may lead to 3 to 8 percent more fuel consumption. Similarly, 1 to 1.5 mm scale build up in the water side may increase the fuel consumption by about 4 to 9 percent. When these occur, boiler heat transfer area should be cleaned. Besides, preventive actions need to be takes to save energy and money.
An efficient energy management system can help you to run your boiler system safely and efficiently.
Benchmark Solutions energy audit team has AEE (Association of Energy Engineers) accredited Certified Energy Auditors (CEB) who are capable of review your boiler, burner, and controls as well as your overall energy management system and make specific recommendations regarding viable boiler efficiency improvements. These improvements will help to run your system safely, reliably and in cost efficient way. Five (5) to twenty five (25%) percent fuel savings in industrial boiler systems is often achievable.
If you want to know more about boiler system efficiency and implement an efficient boiler management system, please contact us today.