With limited space available for the new heater, Inproheat had to custom-design a rectangular tank to fit between the chest end wall and the circulating pump enclosure. The system was completely skid-mounted, assembled, and wired in the factory and included a high pressure combustion air blower and lift pump.
The system is based on Inproheat-patented refractory-less, self-cooling 316L stainless steel combustion chambers. The chambers are light-weight and easy to maintain, without any refractory materials and simply cooled by the vigorous wave action inside the tank.
An 18' long x 10' wide x 9' high carbon steel tank included an internal second-pass heat recovery unit (HRU) and was internally and externally epoxy coated. The outside walls were sprayed with urethane foam insulation and cladded with aluminum.
An Allen Bradley PLC-5 based control system was provided enabling independent control of each burner and fully metered air/fuel ratio control. The system is self-tuning and utilizes ambient air temperature compensation. In case of changes in ambient air temperature, fuel pressure, or tank backpressure, due to foam formation, the control system automatically adjusts fuel air ratio to maintain proper combustion and low levels of carbon monoxide. This control method proved its function in the first few days of operation when the intake combustion air filter froze up, blocking the air flow into the blower suction. The problem was discovered by the operators when the combustion air valves opened fully and the fuel valves closed to low fire. With a typical fixed ratio system, this condition would lead to out-of-ratio firing and unsafe levels of carbon monoxide. In this case the filter was simply removed and within two seconds the system automatically returned to normal valve positions.
The system efficiency was confirmed at 85% by measuring the stack discharge temperature, which is about 20 deg F lower than the water discharge temperature. Due to an obvious efficiency gain and fuel savings, the new SubCom system will be used to handle the base load for the heating process, with the old burners being used only as needed during the cold weather conditions.
As an add-on system, Inproheat incorporated a pH meter to monitor the condition of the process water and to predict the formation of the foam. The defoaming system was also changed to automatic operation. The system continuously monitors the air flow and the air valve opening. A decrease in air flow coinciding with the increase in the air valve opening is interpreted by the PLC as an increase in foam formation and the defoamer solenoid valve opens adding defoaming agent directly to the gas discharge plenum. It is espected that by using defoamer directly and automatically at the critical foaming point, on an as needed basis, will result in significant savings in the defoamer costs.
As an additional feature, Inproheat programmed the PLC to store approximately one week of operational data including fault history. The PLC was interfaced over the data highway to the plant's control room, allowing operators to remotely monitor system's performance. As part of the ongoing service, Inproheat's offering included also a one year system performance monitoring and reporting. Using Symantec PCAnywhere software Inproheat logs periodically (once per week) into the Ainsworth's control system and downloads the operational data history. The data is analyzed and recommendations made regarding system adjustments or operation. Any problems with the PLC program itself or tuning the system can be easily corrected over the telephone line from Inproheat's Vancouver office.
Inproheat's design is based on US-made components, and complies with NFPA, CGA, UL, and CSA requirements. Currently Inproheat owns three US patents and has applied for four new patents related to the above technology system configuration and concept. The Ainsworth SubCom system was started up in December 1999 and turned over to full time operation in mid-January 2000.