Electricity and Control November 2020

PLANT MAINTENANCE, TEST + MEASUREMENT

Optimising boiler performance

Jan-Hendrik Fourie, Bureau Veritas Technical Centre Africa

Boilers and combustion equipment can become an expensive problem for a company if assessments are not conducted on a regular basis to ensure they are performing at optimum levels.Various factors can result in inefficient performance and this can be avoided, saving on unnecessary costs and supporting the life cycle of the equipment.

J an-Hendrik Fourie, Senior Mechanical Engineer at Bureau Veritas Technical Centre Africa, takes a deeper look at boiler and combustion efficiencies and offers insights into improved testing and energy management methods that enable more environmentally sustainable practices in line with BS 845 or ASME PTC 4. The performance of boilers and associated combustion equipment depends particularly on several important com- bustion variables. These include but are not limited to the following: - Air to fuel ratios - Stoker performance, that is: bed heights, grate speeds, flame locations, furnace pressures and related factors - Condition of boiler internals - Effectiveness of draught group, that is: fans and dampers - Moisture content in fuel - Coal particle size distribution - Ash content in coal Over time, the combustion parameters change, and the cumulative effect causes a loss in combustion and boiler efficiencies. Fire-tube boilers with coal-fired chain grate stokers have a design boiler efficiency of about 80%. Over time, the effi- ciency can reduce to 40% or less. There is a direct correla- tion between fuel consumption and boiler efficiency. When a boiler’s thermal efficiency is 40%, the boiler consumes double the amount of fuel to produce the same steam output. It is therefore crucial to perform boiler and combustion efficiency assessments regularly to determine if combustion variables are within specification. It is also essential to reassess a boiler’s performance following ma- jor changes and modifications or when the fuel source has changed. Even if no changes or modifications have been made, it is good practice to perform boiler performance assessments on an annual basis. Boiler owners can also benefit from independent boiler efficiency assessments after commissioning of a new plant or after re-commissioning of a modified plant, to verify com- - Water quality - Air leakages - Insulation - Calorific values of the fuel.

Jan-Hendrik Fourie, Bureau Veritas.

pliance with specifications or contractu- al obligations in terms of performance and efficiency.

It is recommended that a third party is involved to per- form independent boiler and combustion efficiency assess- ments. After efficiency levels have been determined, fur- ther analysis and testing should be performed to determine the root causes of efficiency losses and steam production losses. For instance, if the boiler currently achieves a max of 10 tonnes per hour (tph) steam flow from a 21 tph boiler, investigations can be performed into why the boiler loses capacity and recommendations can be provided to restore efficiency and/or capacity. Calculating boiler efficiencies Trusted third parties, like the Bureau Veritas Technical Centre Africa, assist clients by validating and optimising the boiler performance. Clients can leverage professional expertise in performance testing to detect design flaws or equipment degradation and can then take corrective action to improve boiler performance. There are two methods available to determine boiler efficiency. ƒ With the direct method the major plant inputs required are the fuel consumption and steam flow. Only if both these inputs are accurately measured, can this method be used.

Firetube boilers require regular maintenance to operate at maximum efficiency.

Electricity + Control NOVEMBER 2020

23