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Effect of Low Fuel Oil Temperature on Boiler Operation

written by: Dr V T Sathyanathan • edited by: Lamar Stonecypher • updated: 10/20/2010

Low fuel temperature can lead to a large amount of unburned fuel accumulation in the furnace. This can result in a very high probability for furnace explosion and air pre-heater fires. Maintaining correct fuel oil temperature ensures good combustion of fuel and boiler efficiency.

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    Fuel Oil Temperature and Boiler Operation

    Fuel oil is one of the fossil fuesl used in boilers to generate steam. The hydrocarbons in fuel oil need heating for reducing the viscosity to a favorable level for handling and firing. Depending upon the composition of the oil, the effect on performance of boiler can be judged. All oils should have a viscosity of 80 Redwood No 1 at the burner inlet to result in an effective combustion. The temperature required can be determined by doing a simple viscosity test in a laboratory. It is a good practice to check the temperature required to get 80 Redwood No 1 viscosity for each consignment of fuel oil received.

    The fuel oil is heated in a fuel oil heater using a condensing type heater. The heated oil is then transported though pipe line to the boiler front and distributed to each burner through a set of control, trip, and isolation valves. These pipe lines are generally insulated and heat traced using electrical heating or steam heating. The temperature of the fuel oil at the outlet of the heater is maintained in such a way to take care of the loss of heat in the piping and system so that the viscosity at the gun tip or gun inlet will be 80 Redwood No 1 and below.

    When the fuel oil temperature goes down the operator will have to understand the specific causes, how the plant will respond, what he has to take as an immediate action and how the local operator must respond.

    Specific causes

    • Insufficient steam flow to fuel oil heater
    • Temperature controller of the heater system faulty
    • Excessive condensate in the fuel oil heater lowering heat transfer
    • Faulty steam trap not evacuating the condensate as required
    • Fuel oil heater can be dirty thus reducing heat transfer
    • Too high recirculation of fuel oil from heater outlet to the tank
    • Higher firing rate than design

    Plant response

    • The drop in temperature of fuel oil increases the viscosity leading to poor combustion
    • Black smoke from chimney due to unburned carbon soot carryover
    • Oil particles carryover to air pre-heater and threat of air pre-heater fire

    Immediate operator action

    • Check the pressure and temperature of steam at the inlet of fuel oil heater
    • Restore the steam parameter if required
    • Open steam trap by-pass valve to check for excessive condensate
    • Remove excessive condensate from the heater
    • Reduce the oil recirculation if required
    • Reduce firing rate if needed
    • Bring online additional fuel oil heater to ensure fuel oil temperature with the oil consumption
    • Discontinue oil firing if fuel oil temperature does not come to the required level

    Immediate local operator action

    • Check the fuel oil heater for all its controls and parameters
    • Check steam pressure and temperature to the heater
    • Check the steam trap drains and ensure proper condensate level
    • Inform boiler control room all local findings.

    Irrespective of whether fuel oil is used for load carrying or as support for fuel in a boiler, it is very important to maintain the fuel oil temperature as the amount of unburned fuel collection over a period of time can explode the boiler or lead to air pre-heater fires. Both of this lead to a long outage of the boiler and a loss of production.

    Related Reading

    Poor Oil Gun Performance in Boilers - Oil gun performance can be affected by factors like design, fuel, air distribution, etc. Coal fired boilers have oil guns for start-up and warm-up requirements. Oil fired boilers use them for start-up, warm-up, and load carrying.

    Steps to Evaluate Boiler Explosion - Boiler explosion causes long outage and loss of generation. It can cause loss of life and property. NFPA has collected data on explosion and has large number of standards which guide to prevent explosion. Evaluating the cause, documenting it for corrective and preventive action is essential.

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