Plant & Works Engineering October 2022

26 | Plant & Works Engineering www.pwemag.co.uk October 2022 Energy & Environmental Management Focus on: Boilers, Burners & Controls reaction inside the boiler and potentially problems with water level control and an increase in carry-over. The increase in water leaving the boiler greatly reduces the heat carrying capacity of the pipe since the water cannot impart any heat, it simply serves to restrict the volume of steam that the line can carry. Like many valves, steam trap capacities are linked to the pressure drop across them; lowering the inlet pressure will undoubtedly reduce the capacity of the steam trap; a double- whammy when added to the increased demands on the trap resulting from increased carryover; all steam traps in the system should be assessed for suitability for the lower operating pressure The boiler safety valve is an often over-looked area when considering the reduced pressure. An important point to remember is that the valve is there to protect the boiler and not the downstream system, so it is possible to run a boiler at a lower working pressure without having to alter the safety valve set pressure unless the Competent Person has specifically requested it. When changing the set pressure of a safety valve it is essential that you consult either the boiler maker, or the manufacturer of the valve to ensure its continued suitability since a reduction in set pressure will also mean a reduction in valve capacity. If you find you need a larger safety valve you will also need to change the inlet and outlet pipes to suit. Importantly, the pipes must be sized for the flowrate of the valve at the relieving pressure, NOT the capacity of the boiler (which could be considerably lower) so any calculations of flow capacity must include the pipe arrangement. The inlet line losses must not exceed 3% of the valve set pressure or there is a risk that the valve becomes unstable, restricting the flow through the valve and potentially causing it to close prematurely. Once the valve lifts, the boiler must not increase in pressure by more than another 10%. Most importantly, you MUST notify your Competent Person (the people who approved your Written Scheme of Examination) BEFORE you make any changes. They will expect to see supporting risk assessments and calculations to show that what you are proposing to do is safe and will want to witness at least the final testing as well as update the Written Scheme. So, is it appropriate on your plant to reduce the boiler operating pressure with a view to saving money on fuel costs when you consider both the effects on the plant and equipment and the associated risks of making the necessary changes?