Process reliability relies not only on the quality of the equipment but also the installation and management of the system. Recently we have visited one of our client’s nursery to investigate an issue with their heating system that includes a hot water boiler and a waste oil burner. At the first site inspection, we found black smoke coming out of the stack. It indicated that the burners were running rich that means they were burning too much fuel with not enough combustion air.
The stack on each burner is also too short and had a cowl that was restricting the air flow as shown in the attached image. We have also noticed that the flue ends up very close to the roof line. This will cause atmospheric turbulence in the stack with any sort of wind variation which eventually can make the flame unstable and create intermittent lockouts. The stack needs to be higher to avoid roof turbulence and increase natural draft. The cowl needs to be taken off to increase natural draft and reduce the flue resistance.
The effect of the lack of natural draft was observed when we opened the boiler door. The burner blast tube was disintegrated and diffuser was deformed due to the excess heat. This damage might have been caused by either the burner is struggling to overcome the resistance in the combustion chamber or the position of the draft tube in the combustion chamber.
While firing the burner, we found that during the pre-purging stage the boiler is at a slight negative pressure. However, when the burner is firing it changes to a slightly positive condition. This condition might have been caused by the cowl and the very low natural draft generated by the short stack. It is quite obvious that the draft inside the boiler is not enough to make a stable flame. Also, any wind variation at the stack area could make the situation even more unstable.
By investigating the overall heating system and burner and boiler operation, we found that the draft inside the boiler was not enough and it was largely caused by the stake design and building. It clearly damaged the process equipment, lower the efficiency and increase the downtime. Therefore, it is highly recommended to consult an expert who can assess your plant and suggest a holistic process design along with reliable process equipment.