Last summer, we offered several asphalt mix producers in an area, a site visit to train their people while auditing the status of their operation and as a bonus, fixing problems we had the resources to fix while we were there.
For Flinn Paving, we not only identified problems with their combustion, we fixed them. Whereas, others before us tried to reduce the incomplete combustion, we stuck with fixing it until we did. What made this fix difficult to pin point was the fact that they had two different things contributing to the problem. Material was falling through the flame and the air to fuel arrangement on the burner was set too rich. Both resulted in reading extremely high Carbon Monoxide readings at the stack. Once these two issues were resolved, that burner roared like never before. The combustion intensity at their normal burner position was so great, the burner position was lowered significantly. In so many word, it took less fuel to heat and dry their aggregate.
Our analyzer was showing we were burning nearly all the carbon. As a result, the owner was now working on a positive cash flow that was not available to them before. Saving money is somewhat like a revenue stream.
Controls have evolved since this combustion system was put in place. Matt, the owner, wanted better mix temperature control. With an Automatic Damper control, we could maintain the best burner efficiency possible. With better safety interlocks, we could protect personnel and the equipment much better. And so, we built him a system specifically for his needs.
Over the years, older equipment gets hard to maintain because they are outdated and parts are not readily available. And as funny as it seems, Burner Controls and Damper Controls are usually not run in Automatic. The typical, justifiable excuse I hear from plant operators are that the controls over shoot the set point excessively or just don’t work.
Plant Manager, Scott Cartmill, was running his plant with controls that were not designed to be a Baghouse High Temperature Limit. The aggregate temperature was not automatically controlled. The exhaust damper would constantly hunt for set point because the damper actuator control was too sensitive and there was no way to desensitize it.
Plant Operators should not be babysitting adjustments that can be easily replaced with Automation. Plant operators should have a clear mind for other important things they do. Babysitting processes adds to their stress and adds distraction.
The trick is to set the control so it will make small adjustments so as not to over shoot the set point yet fast enough to keep up with process changes.
Many plants have a damper control that uses a Duff Norton Actuator controlled by a Dwyer Photo-Helic (sensitive vacuum switch) . The actuator moves too fast for the delayed correction to be measured by the Photo-Helic. Consequently, the system will hunt. This forces the operator to place his Damper Control Mode to Manual. The draft wanders around when the operator is not babysitting it and fuel is being wasted and this causes material temperature changes. FYI The Draft Set Point is best determined during a burner tune up. Until that has been determined, the operator should experiment with finding the best draft setting by comparing different settings with the highest material temperature. This is should be in your SOP (Standard Operational Procedure).
Our upgrade included that the Exhaust Damper and Burner Control Valves were provided with valve position indicators. During startup, this is allowing the operator to anticipate where to set these valves at without having to wait for the system to respond.
Many of the older burners had one limit switch to help determine that the mechanical firing rate control on the burner was in a low fire position. Much like making sure your foot is off the gas pedal when you start the car. We do not want High Fire Heat to be roaring down the drum to the baghouse. There are two components necessary that need to be in sync with each other, the gas valve and the burner air damper valve.
Our upgrade included that we placed a limit switch on both of those. Plaant Mechanic KevinKesselberg simply took a small sheave with a bore diameter that would fit over each valve shaft end and then tightened the set screw in a position to make the limit arm actuate the switch when the valves reached the Low Fire Position. We not only electrically tied these two limits in series to the Pilot Solenoid Valve, we wired them to an indicator light (Low Fire Position) on the Panel so we can cross check it’s proper operation every time we light up and shutdown. We used single pole limit switches to energize a double pole relay in order to accomplish this.
.Also, to protect the baghouse, we included a High Temperature Limit, UL Approved as a High Temperature Limit in the inlet. A very important improvement.
The Stack did not have a temperature readout. We added one. In the morning, it’s nice to know when your baghouse is warm enough to run. As you are running, you are expecting the baghouse to run with appropriate temperature drop. You won’t know that without Baghouse In and Baghouse Stack temperature readings. Too big of a temperature drop tells a story of why you all of a sudden lost some of your production rate. Any guesses what may have caused that?
Scott was having problems with his Aggregate Temperature reading low. After eliminating all the problems that we felt it could be, it dawned on us that much of the thermocouple body was exposed to cooler outside air. Although the Thermocouple Tip was exposed to the hot aggregate, the cooler pipe shaft was dragging the aggregate temperature reading down 80 degrees. We mounted the thermocouple so the shaft was being warmed up to temperature in the chute. Since the shaft is of softer steel material, we protected it with an angle iron to keep it from wearing out.
And finally, one of the most important things Flinn Paving benefitted from was that their people understood more about the process and the instrumentation. If you were an airline pilot, you would have to be Instrument Rated in order to fly a plane through the clouds to the airport below with nothing but your instruments. Scott Cartmill and Joe Griffin are now Instrument Rated to land that jumbo jet.
Matt Flinn has always put training for his people at the top of his list. Matt has been one of our best patrons to our training. If you want a sampling of the training they receive, please sample what we have to offer.
As you can see, I’ve been doing all the talking. If you care to contribute or debate an issue, please register. I look forward to facilitating a forum where new ideas are always forth coming.
Until we meet again, I hope the stars are aligned in your favor.