More Information on Blowdown Heat Recovery
The Sentry packaged blowdown system serves two primary functions:
- It automatically controls the surface blowdown to maintain the desired level of total dissolved solids (TDS) in the boiler. This allows safe boiler operation while reducing the amount of blowdown to a minimum.
- It recovers the heat from the high temperature blowdown, and transfers it to the incoming cold make-up water. This decreases the amount of fuel which must be burned in the boiler to bring the feed water up to boiler temperature. It also improves deaerator efficiency by reducing surges caused by adding large amounts of cold make-up to the system.
In operation, the Sentry control senses the flow of cold make-up water, and opens the blowdown valve by a proportional amount. Thus, if make-up flow is large, blowdown flow is large; and if the make-up flow is light, the blowdown flow will be commensurate. By adjusting a handwheel on the valve, the ratio between the two flows can be tuned to find the set point where dissolved solids are being flushed out of the system at the same rate as they are being added. A safe TDS level can thus be maintained in the boiler, by this self-powered, entirely mechanical valve.
The Sentry proportioning control also provides for very effective heat recovery since hot blowdown flows only when there is a corresponding flow of cold water (make-up). Since the two flows are always proportionate, 90% or more of the blowdown heat is commonly recovered.
One convenient location
Systems for multiple boiler installations include a flow control valve for each boiler. This allows for apportioning the overall system blowdown between different boilers, which may be operating at different loads. A strainer and sampling valve are also provided for each boiler, with a sample cooler mounted on the system. Thus, all boilers can be sampled at one convenient location.
Sentry blowdown benefits
The heavy duty Sentry blowdown heat exchangers are unique in that they are designed to handle the blowdown on the tube side. This allows many tube side passes, which ensures maximum heat transfer, and maintains high fluid velocities which prevent scaling and fouling. Due to the severe service, tubes are stainless steel, and because of the abrasive nature of the fluid, return bends are fabricated of extra thick material. Since vibration is a common problem with blowdown exchangers, hold down devices are provided to clamp the tube bundle in place.
Each system is equipped with a blowdown outlet thermometer so that performance can be monitored. By logging data regularly, a cleaning schedule can be established for each exchanger.