Wednesday, June 29, 2011

Turbine Inlet Chilling (TIC) with Thermal Energy Storage (TES)


The hot air is lighter than cold air and has lesser oxygen to contribute to the combustion process of the turbine. So, when the summer temperatures rise, gas turbines lose efficiency and power. This results in significant reduction of the electrical output of the turbine. Generally during the summer, the power demand is at its peak and due to hot weather, the output of turbines is reduced and the power producers experience a reduction in performance. Turbine Inlet Chilling (TIC) is considered to be a cost effective solution to this problem.




Traditionally, this problem has been solved by building more power plants and/or power plants with standby generation capacities. Turbine Inlet Chilling Association (TICA) promotes the development and exchange of knowledge related to gas turbine inlet cooling (TIC) for enhancing power generation worldwide. Turbine inlet cooling provides a cost-effective, energy-efficient, and environmentally beneficial means to enhance power generation capacity and efficiency. 


What is TIC?
Typical CT System (source TCIA) 
TIC is cooling of the ambient air before it enters the compressor that supplies high-pressure air to the combustion chamber from which hot air at high pressure enters the combustion turbine.








Why Cool Turbine Inlet Air?
Effect of ambient temperature on output of CT (source TCIA)
The primary reason turbine inlet air is cooled is to reduce or prevent the often significant loss of power output, compared to the rated capacity, of combustion turbines (CT) when ambient air temperature is high. As per TICA, by cooling the inlet air from 100 degree F to 59 degree F, we could prevent the loss of 27% of the rated generation capacity. In fact, if we cool the inlet air to about 42 degree F, we could enhance the power generation capacity of the CT to 110% of the rated capacity. 
TIC allows an increase in air density by lowering the temperature, and thus, helps increase the mass flow rate of air to the CT and results in increased output of the CT.


TECHNOLOGIES for TIC
Many technologies are commercially available for TIC. These technologies can be divided into the following major categories/groups:

  • Evaporation: wetted media, fogging, and wet compression
  • Chillers: mechanical and absorption chillers without or with thermal energy storage (TES)
  • LNG Vaporization
  • Hybrid Systems: combinations of several technologies

Mechanical Chiller systems can cool the inlet air to lower than wet bulb temperature  and when properly designed can maintain any desired inlet air temperature down to as low as 42 degree F, independent of ambient wet-bulb temperature. The chilled water can be supplied directly from a chiller or from a TES (Thermal Energy Storage) tank that stores ice, or chilled fluid. 


Absorption Cooling systems are similar to the mechanical refrigeration systems except that instead of using mechanical chillers, these systems use absorption chillers that require thermal energy (steam or hot water) as the primary source of energy and require much less electric energy than the mechanical chillers. Absorption cooling systems can be used to cool the inlet air to about 50degree F. These systems can be employed with or without chilled water TES systems.

Thermal Energy Storage (TES) can reduce overall capital costs because it reduces the chiller capacity requirements as compared to the capacity required to match the instantaneous on peak demand for cooling. Since the chillers in TES systems are operated during the off-peak period using low-cost electricity for charging the TES tank and have it stored for use the following day during peak demand. Such a system increases the net power capacity during the on-peak period. With a Thermal Energy Storage tank, operators can pull electricity from the grid at night-time hours (and pricing) to chill the water 
Thermal Energy Storage (TES) designed with Phase-change materials like PCM08P and PCM11P can further enhance the efficiency of chilled water storage as PCM08P can be charged by the output of mechnical chillers (42 degree F/ 5.5 degree C) and PCM11P can be charged by the output of absorption chillers (50 degree F/ 10 degree C). Incorporation of phase change materials in TES increases it's total energy storage capacity and provides better temperature control of the storage tank.


Benefits of TIC with TES

  • Increased net power capacity during the on-peak period
  • Stabilized chiller load during on-peak and off-peak period
  • Increased power output
  • Reduced capital cost ($/kW) per unit of power plant output capacity
  • Increased fuel efficiency
  • Increased steam output 
  • Increased power output of steam turbines in combined-cycle systems
  • Improved predictability of power output by eliminating the weather variable.


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