Heat Recovery Systems

OUTPUT CONTROL OF THE EXHAUST GAS BOILER

excess steam is transformed in good boiler water again, thus limiting the make-up water treatment. By using this method, the regulating system is simple and very reliable. Also, full flow of exhaust gas is maintained inside the boiler, thus minimising risk of soot accumulation. The dumpcooler is a heat exchanger, cooled by : a) shipboard installation: sea water -power barges: sea water -power plants: water from engine cooling system. b) air : in power plants. In this case the air cooler for the engine cooling will be enlarged with a section acting as condenser for the excess heat or a separate air blown cooler is installed for cooling the excess steam from the exhaust gas boiler(s)

The heat capacity of the exhaust gas boiler is determined by the heat input. The heat input to the exhaust gas boiler is determined by the engine load. At high engine output, heat production is larger then at low engine output. Therefore the steam production of the exhaust gas boiler will vary between certain limits. Either the installation can accept variations in heat output or there are moments where heat demand is smaller then heat production. Both heat production and heat demand have to be in balance. In periods where this is not the case, heat will have to be dissipated or heat input to the boiler should be reduced. Basically, there are two methods in controlling the heat output of an exhaust gas boiler Here, the full quantity of exhaust gas remains flowing through the boiler. At the moments when heat production is larger than the demand, the delivered steam pressure or hot water temperature in the system will increase. Pressure or temperature are measured and a mechanical valve is opened at a certain set- point. The excess steam is condensed in the dumpcooler and recovered as water going back to the feedwater tank. In this way, the a) by use of a dumpcooler :

b) by use of a gas-side bypass system :

Here, the exhaust gasses are by-passed over the boiler and in this way the heat input is adapted to the heat demand. This method is often more expensive and more sensitive to service andmaintenance.

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