Heat maintenance system
If a steam boiler is not required for a short period, e.g. at weekends or when not in use at night, the heat maintenance system is useful. This keeps the boiler hot at a reduced boiler pressure. By reducing the pressure in the boiler and therefore also the medium temperature, the heat losses during downtimes are reduced.
Technical information: heat maintenance systems for steam boilers
The boiler heat maintenance system essentially has three benefits:
- Fast availability of full steam output within a few minutes
- Avoids ingress of oxygen which prevents idle corrosion
- Avoids the extremely high mechanical stresses involved in cold starting
Heat maintenance coil installed in base of boiler
Heat maintenance via heating coil
In multi-boiler systems or systems that obtain saturated steam from an external steam network for heating of the heat maintenance coil, the heat maintenance system is implemented using a heating coil which is integrated into the base of the boiler. Here, heat maintenance can be controlled via a control valve in the steam inlet with reference to a setpoint pressure, or can also not be controlled.
The main advantage of this variant is the uniform temperature distribution throughout the boiler. It reliably avoids thermal stratification. This reduces the thermal stresses that accompany the changeover from heat maintenance mode to normal mode significantly.
Heat maintenance via a heating coil
|
PI |
Pressure indicator (pressure gauge) |
PICA± |
Pressure transmitter |
PRZA+ |
Pressure limiter |
Heat maintenance via a combustion system
The heat in single boiler systems or the lead boiler of a multi-boiler system for which no steam is available from the network must be maintained by a dedicated combustion system.
As the rated heat input of the burner in this operating mode only needs to compensate for the heat losses in the system, the combustion output control is set to minimum load. In well insulated systems, the combustion system is only enabled once every few hours. In this case, the heat maintenance operation is frequently enabled at roughly 50% of the average boiler operating pressure so it can be started up very quickly.
However, the burner heat maintenance system inevitably has all the disadvantages of frequent burner cycling, such as pre-ventilation losses and mechanical loads.
Furthermore, if the heat maintenance system is active and no steam is drawn for an extended period (several days) temperature stratification occurs inside the boiler which causes additional mechanical and thermal loads when the boiler is fired again.
Heat maintenance via the combustion system
|
PI |
Pressure indicator (pressure gauge) |
PICA± |
Pressure transmitter |
PRZA+ |
Maximum pressure limiter |