In the context of marine boilers, boiler mountings refer to the various valves and other fittings necessary for the proper functioning of the boiler [1]. These components are directly attached to the pressure parts of the boiler and must be carefully designed and positioned for correct operation and accessibility for maintenance [1].
For a water tube boiler, the mountings typically include the following items [1]:
- Safety Valves These are fitted to protect the boiler from overpressure. In water tube boilers, two safety valves are usually fitted to each boiler: one on the steam drum and another on the superheater outlet header. The superheater outlet header valve is set to lift before the drum safety valves to ensure proper blow-off conditions [1].
- Main Stop Valve Mounted on the superheater outlet header, this valve allows the boiler to supply steam to a common line. It also prevents steam from other boilers from flowing back into a damaged boiler in the event of a burst tube. Some main stop valves include an automatic closing device to shut off steam from the main turbines [1].
- Auxiliary Stop Valves These are smaller versions of the main stop valve, designed to isolate the boiler from the auxiliary steam lines. Their purpose is to prevent steam from flowing back into the boiler if damage occurs and to reduce steam temperature as needed [1].
- Feed Check Valves These valves provide final control over the entry of feed water into the boiler. They are non-return valves and must be designed to be screwed down to prevent boiler water from flowing back into the feed line if feed pressure is lost. Main and auxiliary feed checks are fitted, with the main check connected to the economiser inlet header and the auxiliary check on the steam drum [2].
- Boiler Feed Water Regulator This device controls the flow of water into the boiler, maintaining the desired water level. It is installed in the feed line before the main feed check. These regulators can be attached directly to the boiler shell or connected to the steam drum or boiler shell via balance connections [2].
- Water Level Indicators Regulations require at least two water level indicators per boiler. These typically include two direct-reading water level gauges on the steam drum and a remote reading indicator at a convenient control position [2].
- Low Water Alarms These alarms are installed to reduce the risk of damage from low water levels, which could result from a burst tube or feed supply failure. They may be mounted internally within the steam drum or externally and can be steam or electrically operated. Some versions also incorporate high water level alarms [2].
- Blow Down Valves Used to enable water to be blown from the boiler to reduce its density. They typically consist of two valves in series; the first valve is fully opened, and the second is cracked open. This arrangement protects the seat of the first valve from damage [2, 3].
- Scum Valves Fitted where there is a potential for oil contamination in the boiler. They are mounted on the steam drum and feature an internal shallow pan, located just below the normal water level, to remove oil or scum from the water surface. These valves discharge into the blow-down line [3].
- Drain Valves These are fitted to headers and other parts to allow the boiler to be completely drained. They should only be operated when the boiler is shut down or off-load, not when it is steaming under load [3].
- Air Vents Located in the upper parts of the boiler and headers to release air when filling the boiler or raising steam [3].
- Superheater Circulating Valves When raising steam, these valves first release air from the superheater and then provide circulation to prevent overheating by allowing sufficient steam to blow off to the atmosphere or a drain system. They are closed only when there is enough demand for superheated steam to maintain the minimum required circulation [3].
- Chemical Dosing Valves Fitted to the steam drum, these valves allow feed treatment chemicals to be injected directly into the boiler [3].
- Salinometer Valves Located in the water drum, these enable samples of boiler water to be drawn for testing and control of feed treatment [3].
- Soot Blower Master Steam Valves Usually mounted on the superheater outlet header, these ensure that the superheater is not deprived of steam while soot blowing tubes [4].
- Pressure Gauge Connections These connections are installed on the steam drum, superheater outlet header, and other necessary points to provide pressure readings. They also include suitable connections for automatic combustion control systems [4].
- Thermometers Fitted in superheater headers and other locations for direct or remote temperature readings [4].