that when one is open the other is closed and vice versa furthermore valve 84 assumes the same position as valve 80 in the preferred embodiment all three of the safety valves 80 82 84 are pneumatically controlled in the preferred embodiment the combustion means 74 is a boiler of novel construction and operation shown in fig2 boiler 74 has a feeder arrangement 86 which controls mixing of daf sludge from pipe 72 with atomizing air from unit 92 natural gas from the natural gas train 88 and combustion air from blower 90 as seen in fig2 boiler 74 also has a unique combustion chamber 94 that terminates with an ash hopper 96 and turnaround chamber 98 the fire tubes 102 allow for three full tube passes and terminate in a flue gas stack 100 that has attachments including a draft control 101 oxygen monitor 103 and and particulate collector 150 to ensure that the emissions from boiler 74 comply with state and federal regulations for air pollution feeder arrangement 86 shown in detail in fig3 sets the desired mixing and burning conditions and automatically and regularly monitors them mounting plate 104 on the front of boiler 74 has a central hole and three equidistantly spaced holes around it pipe 72 feeds daf sludge through plate 104 to a coaxial gun 106 specially designed to accomodate the high particulate content of the sludge in gun 106 the sludge passes through the inner tube 108 while atomizing.