Boilers steam & water

1. Economizer section of the Waste Heat Recovery Boiler
   Preheats the circulating water before it enters the evaporator tubes. The counterflow principle is applied, i.e., the hottest exhaust gasses meet the heated feed water.
2. Evaporator section of the Waste Heat Recovery Boiler
   Water evaporates and emulsion of steam and water flows back to the boiler. The counterflow principle is not applied since the evaporated steam rises in the tube bank and it would be disadvantageous to let the steam rise against the water flow.
3. Superheater section of the Waste Heat Recovery Boiler
   Superheats the steam for the turbine. The counterflow principle is applied, i.e., the hottest exhaust gasses meet the superheated steam.
4. Heat exchanger
   Preheats the boiler feedwater.
5. Condenser
   The exhaust steam from the turbine and excess steam from the steam system condense and recycle.
6. Condensate pump
7. Cooling water pump
   Seawater.
8. Make-up water pump
   From softener unit.
9. Boiler feedwater pump

1. Steam pressure control
   The pressure control loop adjusts the burner load according the steam demand.
2. Water level control
   A simple control loop will do for a boiler with large amount of water and relatively small steam output. To minimize shrink and swell at start and stop of the burner it would be wise to have two setpoints for the water level. A lower level (abt. 40%) when the burner is stop and a higher (abt. 50%) when it's firing.
3. Economizer inlet temperature control
   The feedwater is pre-heated in order to increase the efficiency of the plant. The circulating water to the exhaust gas boiler heats the feed water and the three-way valve on the inlet to the heat-exchanger controls the temperature. The economizer inlet temperature must never fall below 135°C to avoid corrosion on the economizer tubes.
4. Condenser pressure control
   An absolute pressure transmitter and a controller adjust the cooling-water to the condenser to protect the condensate from being cooled down more than necessary.
5. Condenser level control
   The level controller actuates the condensate outlet control valve.
6. Feedwater tank level control
   The level controller actuates the make up water control valve.
7. Steam dump control valve
   Takes care of excess steam from the waste heat boiler when the steam production exceeds the steam demand.