Teamwork Paves the Way to Unique Burner Modifications to Utilize Biogas

The multiple hearth furnaces (MHF) at the Kansas City, MO Blue River Wastewater Treatment Plant (WWTP) were built in 1966. The original design contemplated almost autogenous combustion of primary sludge. However, changes in Federal and local air pollution regulations made it necessary to reduce both total hydrocarbon and carbon monoxide emissions. In 1992 the MHF was modified to include a “Zero-Hearth” afterburner. By 2007 the combined effect of lower sludge solids due to adding some secondary sludge and a radical increase in the price of natural gas was having a major impact on the operating budget.Twin 900 kW I.C. engines to generate power from biogas were installed in 1992. However, by 2005 the cost of the natural gas that was blended in the biogas to maintain a consistent heating value was negating many of the cost-reductions achieved. Therefore in 2006 it was decided to see if it would be possible to modify the burners in the MHF to burn digester gas. Furthermore, in order to expedite the conversion process, it was decided to investigate approaches that could be done within the confines of maintenance staff and budget thereby eliminating the need for the longer, more drawn out capital expenditure approach which necessitates (1) study, (2) specifications and finally (3) bid and award.The original burners were natural gas only. However, by adding the modification that allowed for the firing of #2 oil, and then further modifying this equipment by removing the oil nozzle and introducing biogas into the oil atomizing air pipe, a biogas flame that could be seen by the existing Ultra-Violet flame detectors was achieved.By June 2007, only 120 days since the effective Notice to Proceed, the furnace was processing sludge with biogas supplying the majority of the auxiliary fuel. This conversion was not without its problems and difficulties, not the least of which was the burner manufacturer's parts list on replacement burners that had been installed 3 years earlier incorrectly depicting the location of the flame detector. Close cooperation and teamwork between team members who had process and theoretical skills in furnace and burner design and the “hands-on” doggedness of plant engineering that fights through equipment malfunctions on a day to day basis brought this project to a successful conclusion. Adding to this was the continuing faith and support of management that the project would eventually be brought to financially rewarding fruition.The paper will take the reader through a step-by-step description of the process including a complete photographic history.