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Burner with Controls

1.1           Scope

Burners with controls are used to provide heat for hot water, steam and thermal oil boilers, heaters and processes. They are widely used in industry and commerce.

A wide range of burners is available, and these are fitted with combustion controls that offer different levels of precision and repeatability of control. A selected range of burner systems designed to recover combustion exhaust gas heat are also available. The Energy Technology List (ETL) Scheme aims to encourage the purchase of products that are able to accurately control combustion and maintain their efficiency over a specified turn down range.

1.2           Definitions

Burners with Controls covers products that are specifically designed to create and burn air and fuel mixtures in a safe, efficient and controlled manner, and to direct the heat released through combustion into a pressurised vessel (or other combustion chamber).

Eight different categories of burners with controls are covered:

1.    Gas fired and dual fuel burners rated up to, and including, 400kW.

2.    Gas fired and dual fuel burners rated between 401kW and 1,200kW.

3.    Gas fired and dual fuel burners rated in excess of 1,200kW.

4.    Oil fired burners rated up to, and including, 400kW.

5.    Oil fired burners rated between 401 kW and 1,200kW.

6.    Oil fired burners rated in excess of 1,200kW.

7.    Gas fired burners designed to operate with external or built-in thermal storage material that recovers exhaust gas heat (of all rated outputs).

8.    Gas fired burners designed to operate with external or built-in exhaust gas recovery heat exchanger (of all rated outputs).

Products that are designed to use liquid or gaseous biofuels are also covered by these categories.

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.3           Requirements

1.3.1       Eligibility requirements 

To be eligible, products shall:

  • Be gas and/or oil fired.
  • Be a forced draught burner.
  • Be fitted with air dampers that fully close on burner shutdown.
  • Automatically respond to changes in heat demand by modulating their output in a continuous manner (or alternatively for oil-fired burners rated up to and including 400kW only, in a step-wise manner across at least three stages of output).
  • Conform to the requirements of the Pressure Equipment (Safety) Regulations 2016 in respect of their design, manufacture and testing procedures, or have an appropriate Conformity Assessment mark.
  • Not use any form of mechanical linkage between the product’s modulating fuel valve, and its air damper or air control valve, to adjust the product’s air to fuel ratio.
  • Be fitted with a burner heat input control system which is amplitude-modulating or frequency-modulating (pulse firing).

To be eligible, products with a thermal input greater than or equal to 1MW, and less than 50MW, shall comply with the minimum requirements as stated in Annex II of the Medium Combustion Plant Directive (EU) 2015/2193 as implemented in domestic law.[1]

In addition, products with a thermal output in excess of 400kW shall:

  • Incorporate a microprocessor based burner control system.
  • Where mechanical dampers are used to modulate the air flow to the burners, they shall be operated by a precision servomotor. The servomotor shall be controlled by a positional or flow based feedback mechanism that automatically adjusts its operation to correct for mechanical wear, valve stiction and hysteresis.
  • Where control valves are used to modulate the fuel flow to the burners, they shall be operated by a precision servomotor. The servomotor shall be controlled by a positional or flow based feedback mechanism that automatically adjusts its operation to correct for mechanical wear, valve stiction and hysteresis. (This requirement shall not apply to pneumatically operated modulating gas valves).
  • Where the product is gas fired or dual fuelled, use a variable speed motor controller (or variable speed drive) to operate its forced draught fan.

1.3.2       Performance requirements

 For product categories 1 to 6, the product shall meet the following criteria:

  • Automatically respond to changes in heat demand by modulating the output whilst adjusting the ratio of air and fuel fed to the product’s burner in a manner that maintains combustion efficiency across the required turndown range and complies with the maximum permitted levels of oxygen and carbon monoxide in the product’s exhaust gases, as set out in Table 1.1.
  • Products shall not exceed the maximum permitted levels of oxygen (O2) and carbon monoxide (CO) in their exhaust gas at each of test points specified in Table 1.1.

Table 1.1    Minimum performance requirements for burners with controls. ​​​​​

 

 

Product category

Minimum turndown ratio

Maximum O2 level at test point

Maximum CO level

High

Mid

Low

All test points

1.

Gas fired and dual fuel burners rated up to, and including, 400 kW

3.33:1

3.0%

4.0%

4.8%

20 ppmv

2.

Gas fired and dual fuel burners rated between 401 kW and 1,200 kW

4:1

3.0%

4.0%

5.0%

20 ppmv

3.

Gas fired and dual fuel burners rated in excess of 1,200 kW

4:1

3.0%

4.0%

5.0%

20 ppmv

4.

Oil fired burners rated up to, and including, 400 kW

3.33:1

3.0%

4.0%

4.8%

20 ppmv

5.

Oil fired burners rated between 401 kW and 1,200 kW

3.33:1

3.0%

4.0%

4.8%

20 ppmv

6.

Oil fired burners rated in excess of 1,200 kW

4:1

3.0%

4.0%

5.0%

20 ppmv

Where the required test points are:

  • High: the burner is operating at 100% of its maximum continuous rating.
  • Mid: the burner is operating at 50% of its maximum continuous rating.
  • Low: the burner is operating at a level corresponding to the specified minimum turndown, which is 25% of maximum continuous rating for 4:1 and 30% for 3.33:1.

And:

  • Dual fuel means that the product can separately burn both gas and oil.

In addition, gas fired and dual fuelled burners with a thermal output up to, and including, 400kW shall incorporate pneumatic or electronic air fuel ratio controls that permit the oxygen levels in the exhaust gases to be adjusted at each of the test points specified in Table 1.1.

For product categories 7 and 8, the product shall meet the following criteria:

  • Automatically respond to changes in heat demand by modulating the output whilst adjusting the ratio of air and fuel fed to the product’s burner in a manner that maintains combustion air inlet temperature as set out in Table 1.2, while operating at 100% of its maximum continuous rating.
  • Products shall not exceed the maximum permitted levels of nitrogen oxide (NOx) in their exhaust gas specified in Table 1.2, while operating at 100% of its maximum continuous rating.

Table 1.2    Minimum performance requirements for burners designed to recover exhaust gas heat ​​​​​

 

 

Product category

Minimum air temperature entering the burner for combustion at 100% of maximum continuous rating

Maximum NOx level at 100% of maximum continuous rating

7.

Gas fired burners designed to operate with external or built-in thermal storage material that recovers exhaust gas heat (of all rated outputs).

75.0% of designed combustion chamber operating temperature

105 ppmv

(Maximum O2 level: 3.0%)

8.

Gas fired burners designed to operate with external or built-in exhaust gas recovery heat exchanger (of all rated outputs).

37.5% of designed combustion chamber operating temperature

75 ppmv

(Maximum O2 level: 3.0%)

1.4           Measurement and Calculations

1.4.1       Measurement standards

Product performance shall be determined in accordance with the procedures and test conditions in the following standards (or equivalent procedures within applicable British Standards:

  • BS EN 676:2003 (as amended), “Automatic forced draught burners for gaseous fuels”.
  • BS EN 267:2009 (as amended), “Automatic forced draught burners for liquid fuels”.
  • ISO 13579-1:2013 (as amended), “Industrial furnaces and associated processing equipment. Method of measuring energy balance and calculating efficiency. General methodology”

1.4.2       Calculation Requirements

Where the product’s turndown ratio is greater than the minimum required, performance at the low and mid test points may be calculated by linear interpolation of the test results. Where operation at the product’s maximum continuous rated output is not possible, performance at the high test point may be determined by extrapolation of test data at two additional test points (e.g. 70% and 90%).

For the avoidance of doubt oxygen levels in the product’s exhaust and combustion air inlet reference percentage shall be presented to one decimal place. Carbon monoxide and nitrogen oxide levels to zero decimal places. For example,

  • a gas fired burner rated in excess of 1,200kW and whose exhaust gases contain oxygen levels of 3.1%, and/or carbon monoxide levels of 21ppmv, at 100% of its maximum continuous rating, would be deemed a fail.
  • a gas fired burner (designed to operate with an external thermal storage material that recovers exhaust gas heat) with combustion air inlet temperature of 74.9% of designed combustion chamber operating temperature would be deemed a fail.
  • a gas fired burner (designed to operate with external or built-in exhaust gas recovery heat exchanger) with a nitrogen oxide level of 76ppmv (with oxygen levels measured at 3.0%), or a nitrogen oxide level of 75ppmv (with oxygen levels measured at 3.1%), at 100% of its maximum continuous rating, would be deemed a fail.

1.5           Verification for ETL Listing

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-certified
  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing
  • Representative testing (see clause 1.5.1)

Further information regarding the first four routes can be found in Guidance Note 5 on the ETL product testing framework[2].

1.5.1       Representative testing

Where applications are being made for two or more products that are variants of the same basic design, test data may be submitted for a representative selection of models, provided that all variants:

  • Are designed to burn the same fuel(s) as the representative models.
  • Have the same basic constructional design as the representative models.
  • Use the same burner control system / mechanisms as the representative models.
  • Have the same or better energy efficiency as the representative models. It should be noted that:
    • If a manufacturer voluntarily removes the representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL.
    • If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative model will be removed from the ETL.

1.6           Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.


[1] The Environmental Permitting (England and Wales) (Amendment) Regulations 2018

The Pollution Prevention and Control (Scotland) Amendment Regulations 2017

The Pollution Prevention and Control (Industrial Emissions) (Amendment) Regulations (Northern Ireland) 2018

[2] https://www.gov.uk/government/publications/energy-technology-list-etl-product-testing-framework