Steve O’Neill, Technical Specifications Engineer at EOGB Energy Products Ltd, explains the importance of regular burner maintenance and the correct procedures to ensure optimum efficiency and safety.

 

Manufacturers of most gas and oil burning equipment recommend regular maintenance and safety checks for their respective products in order to achieve optimum levels of safety and efficiency. This will typically include the necessity to confirm:

 

  • An adequate supply of combustion, cooling and dilution air
  • Correct burner, operating pressure and gas rate/heat input
  • The effectiveness of any flue
  • Safe function of the plant and confirmation that it will always fail to a safe situation.

 

Failure to ensure any of the above factors could have the effect of causing incomplete combustion and/or cause plant failure potentially incurring injury to personnel and/or large financial losses.

 

By implementing a suitable maintenance programme for the plant it is possible to avoid potential breakdowns before they occur, as the maintenance will inherently involve the visual inspection and cleaning of the plant components, allowing a good opportunity to replace or adjust accordingly without incurring periods of down time at a later date. Furthermore, optimum efficiency is maintained throughout the operating time of the plant.

 

 

Visual inspections

 

Air supply

 

In order to ensure complete combustion of a fuel, an adequate supply of oxygen (O2) must be present to oxidize all the fuel (O2 for combustion is usually taken from the atmosphere). It is understood that the air in the atmosphere consists of approximately 77% by mass (79% by volume) of nitrogen (N2) and 23% by mass (21% by volume) of O2.

 

Depending on the design of the appliance the H2O can be either in a liquid or vapour state within the combustion products.

 

The provision of suitable combustion air should be confirmed on every inspection with all restrictions and debris being removed accordingly.

 

Inspection of the flue throughout its route

 

In addition to the confirmation of a satisfactory supply of combustion air etc the flue should be visually inspected at regular intervals to confirm all products are being evacuated effectively, that the flue is adequately supported, there is no evidence of mechanical failure and that the flue is terminating satisfactorily.

 

Gas rate

 

A gas rate should be carried out to confirm the correct volume of fuel is being delivered to the appliance thus ensuring the plant is capable of providing the prescribed energy release that it is designed for. If the gas rate lies outside the scope the plant was designed for it would result in both a loss in efficiency and potentially incomplete combustion as well as potential damage to the plant and ancillary equipment. The gas rate/burner pressure is checked on almost all routine maintenance visits and the necessary adjustments can be made to return the plant to optimum operation.

 

Combustion analysis

 

The ability to interpret the information being provided by an electronic combustion analyser can be a critical factor in ensuring both optimum efficiency and combustion safety. Furthermore the engineer should be able to discern when it is necessary to rely upon the combustion ratio to confirm correct operation and when to read the O2, CO2, and CO. For example:

 

 

Equation 1.1

 

CH4 + 2O2 +{ × 2 = 7.52N2} Þ CO2 + 2H2O + 7.52N2

 

 

It is possible to identify from the equilibrium equation 1.1 that for a specific fuel complete combustion will yield a fixed percentage of CO2 and H2O when a given volume of gas is burned in theoretical air. It is also a fact that any deviation in the quantity of air from that of theoretical value will alter the quantity of CO2 produced and a resultant effect on combustion efficiency will follow.

 

Any increase in the amount of combustion air will result in a reduction in CO2, as the increased volume of air will dilute the quantity of CO2 within the products, thus reducing both flame temperature and overall combustion efficiency. The common definition of this additional air above theoretical is known as excess air.

 

Conversely if the combustion air is reduced from that of stoichiometric this would give rise to a situation where there would be inadequate air to completely burn of all the fuel, which would allow the formation of dangerous CO and other unburned hydrocarbons (UHC’s). It can also be observed that it is not possible to balance the chemical equation with CO2 and H2O.

 

CH4 + O2 Þ CO2 + CO +H2O + H etc

 

Although a significant quantity of CO2 can still be produced with the absence of enough combustion air, the remaining fuel will compete for any remaining O2 leading to the formation of differing species in various quantities.

 

It can be observed from the statement above that the higher the CO2, the more efficient the combustion.

 

However it cannot be assumed that by simply increasing the CO2 value we can confirm optimum efficiency or safety and indeed due to the higher flame temperature a dissociation of the combustion products would follow resulting in the production of CO and other UHC’s.

 

It becomes evident that it is a necessity to incorporate a quantity of excess air. This must be monitored on a regular basis as the plant equipment can have a propensity to drift over time. Regular maintenance will provide an opportunity for minor adjustment and will ensure sustained periods of optimum operating efficiency whilst maintaining safety at all times.

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