Technical Manual - Section 3 (Safety Hazards)

pressure, the heater stream could enter into the process fluid.
If loss of circulation occurs in liquid or gas coolers, increased
product temperature could affect downstream operations and
require pressure relief.
Health
Because these are closed systems, exposures under normal
operating conditions are expected to be minimal. Depending
on the fuel, process operation, and unit design, there is a
potential for exposure to hydrogen sulfide, carbon monoxide,
hydrocarbons, steam boiler feed-water sludge, and
water-treatment chemicals. Skin contact should be avoided
with boiler blowdown, which may contain phenolic
compounds. Safe work practices and/or appropriate personal
protective equipment against hazards may be needed during
process maintenance, inspection, and turnaround activities
and for protection from radiant heat, superheated steam, hot
hydrocarbon, and noise exposures.
STEAM GENERATION
HEATER AND BOILER OPERATIONS
Steam is generated in main generation plants, and/or at
various process units using heat from flue gas or other
sources. Heaters (furnaces) include burners and a combustion
air system, the boiler enclosure in which heat transfer takes
place, a draft or pressure system to remove flue gas from the
furnace, soot blowers, and compressed-air systems that seal
openings to prevent the escape of flue gas. Boilers consist of
a number of tubes that carry the water-steam mixture through
the furnace for maximum heat transfer. These tubes run
between steam-distribution drums at the top of the boiler and
water-collecting drums at the bottom of the boiler. Steam
flows from the steam drum to the superheater before entering
the steam distribution system.
HEATER FUEL
Heaters may use any one or combination of fuels including
refinery gas, natural gas, fuel oil, and powdered coal.
Refinery
off-gas is collected from process units and combined with
natural gas and LPG in a fuel-gas balance drum. The balance
drum provides constant system pressure, fairly stable
Btu-content fuel, and automatic separation of suspended
liquids in gas vapors, and it prevents carryover of large slugs
of condensate into the distribution system. Fuel oil is
typically a mix of refinery crude oil with straight-run and
cracked residues and other products. The fuel-oil system
delivers fuel to process-unit heaters and steam generators at
required temperatures and pressures. The fuel oil is heated to
pumping temperature, sucked through a coarse suction
strainer, pumped to a temperature-control heater, and then
pumped through a fine-mesh strainer before being burned.
In one example of process-unit heat generation, carbon
monoxide boilers recover heat in catalytic cracking units as
carbon monoxide in flue gas is burned to complete
combustion. In other processes, waste-heat recovery units
use heat from the flue gas to make steam.
STEAM DISTRIBUTION
The distribution system consists of valves, fittings, piping,
and connections suitable for the pressure of the steam
transported. Steam leaves the boilers at the highest pressure
required by the process units or electrical generation. The
steam pressure is then reduced in turbines that drive process
pumps and compressors. Most steam used in the refinery is
condensed to water in various types of heat exchangers. The
condensate is reused as boiler feedwater or discharged to
wastewater treatment. When refinery steam is also used to
drive steam turbine generators to produce electricity, the
steam must be produced at much higher pressure than
required for process steam. Steam typically is generated by
heaters (furnaces) and boilers combined in one unit.
FEEDWATER
Feedwater supply is an important part of steam generation.
There must always be as many pounds of water entering the
system as there are pounds of steam leaving it. Water used in
steam generation must be free of contaminants including
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