Heater controls
A burner management system is required for automatically-ignited fuel burners. Traditionally, a very simple, economical burner management system is used for the burners on direct-fired tanks. It opens the fuel valve and ignites the fuel when the thermostat calls for heat and closes the valve when the thermostat is satisfied. It has a sensor that shuts off the fuel if it does not detect the presence of a flame. This type of system works very well on direct-fired tanks because the burner does not usually cycle frequently.
On hot oil heaters the burner management system is usually more sophisticated. It uses a microprocessor to manage the burner controls and provide proper burner sequencing, ignition, and flame monitoring protection.
A control panel mounted on the heater houses key electronic components (Figure 57). Readouts and signal lights on the face of the panel indicate the current burner status and its operating history.
Figure 57. Heater Control Panel With Readouts And Status Lights.
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If a problem occurs that causes the burner to shut down, the lights identify all switches affected by the shutdown. You can normally tell from the lights which limit switch tripped first, setting off the chain reaction that caused the shutdown.
The control panels should always be UL approved and may be either NEMA 4 or NEMA 12. NEMA 12 panels are dust tight. But NEMA 4 panels give added protection and are preferred. They protect against windblown dust and rain, splashing water and hose-directed water.
Emissions
A blue smoke condenser is a heat exchanger sometimes used as a vent in tanks of heated asphalt cement to minimize air pollution (Figure 58). It condenses gas vapors, commonly known as blue smoke, produced by heating light ends (volatile organic compounds) often present in the liquid asphalt cement. Condensing the vapors turns them into a liquid state wherein they return to the liquid asphalt cement instead of escaping into the atmosphere through the tank vent or exhaust stack.
Figure 58. Blue Smoke Condenser Minimizes Air Pollution.
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Condensers used on asphalt storage tanks usually have a number of tubes with external fins. The tubes are cooled by ambient air circulating through the fins. Thus, gasses exiting the tank are cooled as they flow through the tubes. The cooling causes vapors of the VOCs to condense and to drain back into the tank. This greatly minimizes the release of pollutants into the atmosphere.
Containment
Containment refers to a secondary enclosure for tanks that contain liquids, usually fuel or asphalt cement. It functions to keep the liquid from escaping in the event of a leak or rupture in the primary tank. The main concern is for the environment. However, a containment can also minimize the impact that an accidental spill can have on operation of the HMA facility.
Containment enclosures are often no more than concrete walls built around a group of tanks (Figure 59). However, Heatec offers containment enclosures for individual tanks fabricated from steel (Figure 60). On portable tanks the containment enclosure consists of a second tank that fully encloses the main tank—a double-walled tank. On a stationary or relocatable tank the containment enclosure usually encloses only the bottom portion of the tank.
Figure 59. Concrete Wall Containment Encloses Several Tanks.
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Figure 60. Tank With Built-In Containment Shell.
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