Firing Capacity Control

Water Circulation Measurement




General


The water circulation in natural circulation boiler plants influences the operating result significantly as well as the operational safety. The performance reserve of a boiler plant can be used subject to all security related aspects by a flow monitor (patent DE 19962429 A1) the performance reserve of a boiler plant can be used under qualified consideration of safety relevant aspects.


Limiting Factors




Performance reserve


The rising cost pressure in power plant manufacturing led to the demand of increasingly higher capacity at equal construction volume. Due to the improved water circulation calculation the pressure bodies will be designed closer referring to the operation point. The design of new plants aims at having less performance reserves and operating close to the maximum power point. Operators of older plants are striven to exploit the performance reserves of their plants.

Complexity of the two-phase flow


The physical models of the two-phase flow show calculation inaccuracies still, wherefore calculation uncertainty exists, that has to be considered by corresponding security surcharge.

Modified flow properties by water conditioning


Water conditioning for corrosion protection causes a modification of foam, which results in the flow form and the friction of the two-phase flow in the tubes.

Operational influences


Some operational parameters, that were unknown during the design stage, influence the water circulation, especially pressure, load and feedwater temperature fluctuation.


Functional principle

  • The flow monitor is based on an ultrasonic flow measurement device.
  • The measuring heads will be flanged in boiler zones, where the most endangered zones were predicted based on water circulation measurements.
  • The measurement device does not show quantifiable values for water and steam velocity, but a qualitative evaluation criterion about the flow condition.
  • Before the break-away of the cooling water film, that enters at stratified and wavy flow in horizontal tubes and droplet flow in vertical tubes, a warning signal will be given to the control room by the flow monitor.
  • Operating the boiler close to the maximum capacity is possible by coupling the measurement signals with the firing capacity control.

Fields of utilisation


This technology can advantageously be used at all natural circulation boiler types, which means a large market potential. Boiler systems firing inhomogeneous fuels (waste incineration and processes with heavy wavy steam taking, e.g. paper industry) are predestined for the use of a flow monitor. It should be placed in endangered zones like horizontal tubes or in areas with unsafe flow conditions (small boost with heavy heat load), especially.


Product characteristics

  • Simple installation of the measuring heads by clamp-on method,
  • No influence on the tube flow due to contact-free measurement,
  • Minimal maintenance,
  • Avoidance of boiler damages,
  • Increased availability,
  • Use of the energetic reserves of the boiler,
  • Increased operational flexibility
    (pressure decrease and part loads).