Piping
Make sure that you include a bypass circuit in your thermal fluid piping to the preheater. This will allow you to shut off thermal fluid to the preheater for maintenance without shutting off thermal fluid to asphalt tanks or other plant components.
Figure 8. HFP preheater inlets and outlets.
A bypass circuit can be created by installing two three-way valves: one at the thermal fluid inlet valve (B, Fig. 8) and one at the thermal fluid outlet (H, Fig. 8) and connecting them with a bypass line. In any case, be sure to include a valve to prevent thermal fluid from flowing backward into the preheater thermal fluid outlet (H, Fig. 8). Otherwise, thermal fluid will spill when the preheater inlet and outlet connections (A and I, Fig. 8) are removed for maintenance. Valves should be as close as possible to the preheater inlet (B, Fig. 8) and outlet (H, Fig. 8) to minimize the amount of thermal fluid to be drained for preheater maintenance.
Install a fuel pump in the fuel inlet piping to the preheater. If the fuel pump is installed in the outlet piping, the pump may cavitate and fail. Make sure you install shutoff valves in the piping for the fuel inlet and outlet to minimize fuel spillage when the heating coil assembly is removed for cleaning.
For thermal fluid pipe connections use only piping with welded flanges. Do not use threaded connections. Supply and return lines should be at least 1-1/2 inch in diameter. You may need flex hoses to compensate for thermal expansion and alignment of pipe flanges.
Piping with welded flanges is also preferred for fuel lines, but threaded fittings are acceptable.
Bypass relief valves and pressure relief valves require different piping, so note which type of valve is provided on your preheater.
The difference between bypass relief valves and pressure relief valves:
Early model preheaters were fitted with bypass relief valves (Fig. 9). Current models are fitted with pressure relief valves (Fig. 10). Preheaters with code stamp (optional) are fitted with pressure relief valves that meet code ASME VIII.
Bypass relief valves are designed with an opening at the valve seat that allows continuous flow of fuel, even at pressures less than the set pressure of the valve.
Figure 9. Bypass relief valve used on early model preheaters.
Pressure relief valves are sealed. They only open when internal pressure rises above the set pressure of the valve. When open, the valve releases a small quantity (a few ounces) of fuel until pressure is released.
Figure 10. Pressure relief valve used on current preheaters.
For preheaters with bypass relief valves: Install a fuel line from the bypass relief valve on the preheater back to the fuel tank. Failure to do so will result in continuous fuel leakage from the bypass relief valve.
For preheaters with pressure relief valves: Install a pipe from the outlet of the pressure relief valve to a point about 10 inches above the ground. Leave enough space to place a bucket under its end to catch any fuel that escapes.
Note: Skid-mounted preheaters already have a fuel overflow pipe attached to the pressure relief valve (Fig. 11) and require no additonal drain pipes.
Figure 11. Fuel overflow pipe attached to the pressure relief valve on a skid-mounted preheater.
| Important Notice
By design, overpressure can only occur if the fuel valves at the inlet and outlet (C and F, Fig. 8) are closed and heating is activated. Therefor, ALWAYS make sure fuel valves are open when starting up preheater.
|
|
|
Electrical connection
Wiring diagrams of the preheater controls are provided separately, either in the control panel or in a separate binder. The electrical power source for all preheaters should be a branch-circuit breaker that is dedicated to the preheater.
For stand-alone HFP preheater:
Provide an earth-ground to the ground lug provided in the preheater control panel. Provide 120 volt / 1 phase / 60Hz power to the power supply located inside the panel.
Install a set of auxiliary contacts on the motor starter for the fuel pump. Typically, the motor starter is located in the plant’s control house. Connect the auxiliary contacts to the proper terminals in the preheater control panel.
For skid-mounted HFP preheater:
Provide earth-grounds to the ground lugs provided in the preheater control panel and the power panel for the fuel pump motor starter. Provide 480 volt / 3 phase / 60Hz power to the power supply located inside the power panel for the fuel pump motor starter.
For stand-alone HFP-E preheater:
Provide an earth-ground to the ground lug provided in the preheater control panel. Provide 480 volt / 3 phase / 60Hz power to the power supply located inside the preheater control panel.
Install a set of auxiliary contacts on the motor starter for the fuel pump. Typically, the motor starter is located in the plant’s control house. Connect the auxiliary contacts to the proper terminals in the preheater control panel.
For skid-mounted HFP-E preheater:
Provide an earth-ground to the ground lug provided in the preheater control panel. Provide 480 volt / 3 phase / 60Hz power to the power supply located inside the preheater control panel.
Final
Make sure to set the main power disconnect switches on all preheater panels to OFF before activating power to the preheater.
This completes installation, and the preheater is ready for operation.
← previous
