Local district heating systems should lie within the range of 40-60 MW. The effect refers to the actual heat requirement in the buildings. The combined heating and power plant should deliver about 60% of the total connected heat requirement, at optimum distribution between electricity (40%) and heat production (60%). Minimum output, electricity and heat, is to be 200 MW.
The local heating plants should be connection to a combined heating and power plant only be used at peak loads and at operational break down and maintainance the combined heating and power plant.
Existing boilers, of 40-60 MW, in good condition that do not need to be exchanged within a reasonable time, should use coal with a low content of ashes, the combustion should be made with a high efficiency. Flue gas coolers should be installed to raise the effictively and then the condensate, SOx must be taken care of effectivly. The boilers should be in operation night and day and turned off only for cleaning.
Flue gas purification with bag filter should be installed, and as maintenance work is required, other measures should be taken for a change-over to the supply from a combined heating and power plant.
In principle, the same procedure applies on both smaller and larger boilers, but the smaller ones should be removed as soon as possible, and their system is to be connected to larger plants with flue gas purification.
When new boilers are installed, either in new or existing district heating networks, the out put should be of about 40-60 MW, the combustion should be made with a fluidised bed. The coal quality has to be good, i.e. low contents of sulphur and ashes, and the combustion should be done continuously as long as there is any need of it. Two or more local heating plants of this size can at an early stage be connected to preinsulated pipes. It is better to have one heating plant with a capacity of 100% in operation, than to have three with a capacity of 33% each.
The discharges of SOx and NOx stays at an acceptable level with this combustion technique, even without purification. When the local heating plants are later connected to the combined heating and power plant, the operation times will be reduced to perhaps 15-20% per year, the SOx -and NOx levels are then acceptable.
The discharges of particles must be limited. This is done by using bag filters.
|Title:||8 STEPS – CONTROL OF HEATING SYSTEMS – Part 5 – Instructions for designing district heating systems|
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