Boiler Economizers

Boiler Economizers

Studies have shown that over a 20 year period, 96% of the cost of operating a boiler system comes from fuel costs. Also, in a typical boiler system, 10% to 20% of energy input is lost in the form of heat escaping to the atmosphere. The installation of a boiler economizer helps to solve this problem. An economizer is a unit that captures heat from the stack, and then returns it to a water system. To determine if a boiler economizer is right for your facility, look at your annual boiler fuel bill and subtract 5 to 10% of the cost. If this is a significant number to you, then you should consider adding an economizer. The payback will have a direct impact on your bottom line. This is one of Cannon’s many products that help companies reduce overall energy consumption. And remember, fuel not burned equals exhaust gasses not emitted!

Three major parameters are considered in evaluating all boiler economizers; 1) fuel type, 2) acceptable backpressure on the exhaust, 3) inlet water temperature.   These will determine which of our following heat recovery product is best for you.

  • Feedwater Heater – normally used on small boilers burning natural gas, and non-condensing flue gas environments. Inlet temperatures 150F to 250F
  • Gas Condensing Water Heater – normally used on small and large systems burning natural gas, and condensing flue gas environments. Inlet temperatures 40F to 150F
  • Heavy Duty Economizer – normally used on large systems burning dirty fuels, and non-condensing flue gas environments. Inlet temperatures 200F minimum
  • On-Demand Economizer – fits where other systems will not. Normally systems burn natural gas, and condensing flue gas environments. Inlet temperatures 40F to 150F
  • Dual Stage Economizer – used for heating two separate streams with the same economizer. Can be used on small and large systems burning natural gas, and condensing or non-condensing flue gas environments. Inlet temperatures 40F to 250F

What is the difference between a regular boiler economizer and a condensing economizer? The difference is the temperature range in which the economizer is operated. Our units may look identical in outward appearance, but can be used in a condensing application if originally design to do so. A traditional economizer is operated in a hot environment, the tubes and the flue gases are well over 200°F. A condensing economizer operates in a cool environment, where the tubes and flue gasses may be well under 200°F. A large savings increase occurs when the flue gas temperature is decreased to under 135°F, but this is only effective when burning natural gas and have the correct materials of construction.

Can HD Economizers be used on hot water boilers? Yes, although they are sized differently on hot water vs. steam boilers. Normally due to their high flow rate, boiler economizers are designed for this flow imbalance. Still, efficiency gains in the range of 2 – 5% are possible.

CBW’s boiler economizers come standard with SA178 Grade A carbon steel boiler tubes. In some cases there are the potential problems with austenitic stainless steel tubes, Type 304 and 316. This grade is typically not used in HD economizers. Stress corrosion cracking of austenitic stainless steel eliminates its use in ASME Section I pressure vessels. Chloride levels in the water, or halogen compounds in the flue gas, can cause tube leaks in a very short time. Many studies can be found on-line on the subject (search: stainless steel SCC). We offer duplex stainless steel tubes to combat this problem.

The customer doesn’t have available budget or money … Many of our customers have found they can install a feed water heater on a maintenance budget or by using outside financing. Customers need to identify the money they are losing ever year if they don’t have an installed gas condensing water heater. Many times the installation of an economizer is a cash positive transaction when the cost is financed.

It won’t fit under the roof or through the door of our boiler room … CBW provides options for its feed water heaters so that they can be installed outdoors. Our units can be installed vertically or horizontally, or floor mounted with an added ID fan. The system can also be field assembled for installation at almost any site.

Can CBW provide piping and installation assistance? YES, we have some standard piping diagrams available for email to our customers. These are only suggestions, as every installation is slightly different in the existing equipment and available space. Also, our knowledgeable representatives, located nationwide, are experienced in makinginstallation issues disappear.

In all cases, we wish to have water flowing through our boiler economizer whenever the burner is on; therefore provisions have to be made for circulation through our heat exchanger and back to an existing tank when the burner is on. We can guide you through the three methods for doing this; 1) Manual valve or set orifice plate, 2) Spring loaded pressure regulator, 3) Solenoid valve as slave from boiler feed valve.

What pressure should the safety valve be set at? Our boiler economizers are normally designed and ASME Code stamped between 400 and 700psig. We supply the valve matching the unit design pressure as a default. At a customer’s request, we can set the valve lower (matching existing boiler) or higher (requires Code calculations at extra cost).

What are CBW’s standard materials of construction? Tubes: CBW’s units come standard with SA178 Grade A boiler tubes. Several grades of stainless steel are available as upgrades, depending on potential corrosion problems and operating temperatures, such as 304SS, 316SS, Duplex SS, AL6XN.

Fins: CBW’s units come standard with low carbon steel fins, with nickel brazed fin attachment to the tube.

Also available are 409SS, 304SS and 316SS depending on potential corrosion problems and operating temperatures.

Frame: CBW’s standard frames are made of carbon steel angle iron, and are available in 304SS depending on potential corrosion problems and operating temperatures

Removable side panels: CBW’s standard units include 16 ga. 304 stainless steel lining, two inches of insulation, and 16ga. carbon steel painted exterior.

Transitions: CBW’s standard units include 10 ga. carbon steel painted exterior. Thicker carbon steel is available to support extra weight, and 304 stainless steel is available for potential corrosion problems.

Do we have to insulate CBW’s unit in the field? The removable side panels are insulated. The piping and transitions should be insulated by the installer. We do not offer additional insulation for the transitions because it may not survive during shipment.

What are the potential problems with austenitic stainless steel tubes, Type 304 and 316? Stress corrosion cracking of austenitic stainless steel eliminates its use in ASME Section I pressure vessels. Chloride levels in the water, or halogen compounds in the flue gas, can cause tube leaks in a very short time. Many studies can be found on-line on the subject (search: stainless steel SCC). We offer duplex stainless steel tubes to combat this problem.

What is duplex stainless steel used in CBW’s tubes? ASME SA789 type 2205 duplex stainless steel is a homogeneous mixture of austenitic and ferritic stainless steel. It is acceptable for ASME Section VIII units and has better corrosion resistance than 300 series stainless steels in most applications. We have had great success with this grade of tubes in our units, as they normally last the life of the boiler system. Many studies can be found on the internet on this subject, (search: duplex stainless corrosion)

Does CBW’s unit come with a bypass damper? Our standard offer does not include a bypass damper, as we want to recover heat 100% of the time that the boiler is operating. An integral bypass is available in cases where it is needed. Our On-Demand unit has a bypass damper system included.

What is the difference between a regular economizer and a condensing economizer? The difference is the temperature range in which the economizer is operated. Our units may look identical in outward appearance, but can be used in a condensing application if originally design to do so. A traditional economizer is operated in a hot environment, the tubes and the flue gases are over 200°F. A condensing economizer operates in a cool environment, where the tubes and flue gasses may be well under 200°F. A large savings increase occurs when the flue gas temperature is decreased to under 135°F, but this is only effective when burning natural gas. Potential corrosion of the stack downstream can be addressed by upgrading the materials of the stack.

Can feed water heaters be used on hot water boilers? Yes, although feed water heaters are sized differently on hot water vs. steam boilers due to their high flow rate. Still, efficiency gains in the range of 2 – 5% are possible.

What does CBW have available for small boilers under 100 HP? The FB-4 unit is designed as a universal economizer for boilers under 100 HP. It is lightweight and easy to install.

What ASME code stamp applies? Units are typically designed for Section 8 Division 1 on indirect fired pressure vessels. Normally, Section 1 is not available due to the need for stainless steel tubes in condensing applications. Section 1 does not allow stainless steel tubes.

The customer wants to avoid condensing of the flue gas, regardless of the fuel being burned …CBW designs its feed water heaters with proper materials and a water removal system so that condensing is not harmful to the boiler system or economizer. Condensing is always avoided when heavy fuels are burned.

The customer doesn’t have available budget or money … Many of our customers have found they can install a feed water heater on a maintenance budget or by using outside financing. Customers need to remember that they’re losing money every year they don’t have a unit installed. Many times the installation of an economizer is a cash positive transaction, even when the cost is financed.

I don’t want to have to maintain another piece of equipment … The life expectancy of a properly designed feed water heater far exceeds the life of a boiler.

How will the feed water heater affect my upstream and/or downstream equipment? I don’t want it to shut down the boiler system … CBW properly designs its feed water heaters for the boiler/burner combination. As such, overall downtown and the potential for unscheduled outages are reduced. If maintenance is required, the economizer can be taken out of service and the boiler can continue to operate until a shutdown can be scheduled. It’s important to note that CBW’s feed water heater design can be repaired quicker than any competitor designs.

It won’t fit under the roof or through the door of our boiler room …CBW provides options for its feed water heaters so that they can be installed outdoors. Our units can be installed vertically or horizontally, or floor mounted with an added ID fan. The system can also be field assembled for installation at almost any site.

 

For More information on Boiler Economizers call 724.335.8541 or click here to contact us.

Cannon Boiler Works Economizer Line