Veolia Bordeaux was integrating a new turbine with district heating in their waste incineration plant. There is a district heating heat exchanger in the turbine exhaust, supplying 22MW of heat to the city of Bordeaux. Bronswerk Heat Transfer designed the control system to ensure effective heat distribution for district heating and optimal turbine backpressure for maximum power generation. We supplied the Air-Cooled Condenser, District Heating Heat Exchangers and relevant additional equipment. As a result, the system operates flawlessly with a smooth response to changes in heat demand.
The customer requires maximum output of district heating in winter while decreasing the turbine exhaust pressure in summer to obtain maximum turbine efficiency. Because both Condensers - Water-Cooled and Air-Cooled district heating - are in the same outlet stream, how do we guide the steam in the right direction? How do we control the pressure? In the original P&ID there where butterfly valves foreseen in the steam duct, and separate condensate packages for both the district heating Heat Exchanger and Air-Cooled Condenser
Instead of diving into the detailed design of the heat exchange equipment itself, our thermal and process engineers first looked at the whole picture. What are the objectives of the system? How is the system controlled? When would the customer meet their targets?
We quickly concluded that controlling the steam flow with valves is not the most reliable solution, because butterfly valves are not known for their optimal controlling range. Also, why operate with two condensate packages if the maximum steam flow is constant anyway and will only be distributed between the two
First, we let physics work for us: steam is attracted to cold surfaces. We can make the Air-Cooled Condenser attract less or more by varying the air flow. Second, the water-cooled condenser could become self-controlled on water outlet temperature. Finally, we used an ingenious system to allow the condensate from both exchangers to run into the same condensate tank, without risking backflow in either summer or winter operation.
This resulted in a system that operates smoothly and exchanges heat load from the district heating towards the air-cooled condenser.
- CAPEX saved one instead of two condensate packages and butterfly valves.
- Integration of both services in one steam/condensate system resulting in lower OPEX.
- 100% transient flow and pressure fluctuations.
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