During the course of treating a fluid, for instance to control the atmospheric emission of polluting contaminants, it is common to disperse a treating agent into the fluid in order to combine with a catalyst to treat the undesired component of the fluid. In general, a mixing apparatus is used to disperse the treating agent into the fluid. Holes, which include hardened holes, holes, nozzles, injection nozzles, and the like, can be used for this purpose. Since simple ejection of the agent from such holes is not very effective in thoroughly mixing the agent with the fluid, it is also known to use baffles (sometimes also referred to as “deflectors” and “flow mixers”), usually positioned directly downstream of the injection point to encourage turbulence, thereby enhancing the mixing of the agent with the fluid.
One of the applications of the mixing apparatus is the treatment of flue gas containing nitric oxide and nitric dioxide (collectively, “NOx”) and other hazardous chemicals produced during the combustion of fossil fuels. NOx emissions may be minimized by catalytically reducing flue gas NOx to nitrogen and water using ammonia (NH3) in a chemical reaction before releasing the gas into the atmosphere.
Flue gas may be treated by passing the gas through treatment systems, which attempt to provide maximum exposure of the catalyst to the flue gas in order to ensure that all the flue gas comes sufficiently into contact with the catalyst for treatment.
In the treatment systems, a treating agent, such as ammonia, is typically introduced into the flue gas stream by the mixing apparatus comprised of pipes having a plurality of holes. The mixing apparatus is designed to provide an even distribution of ammonia throughout the flue gas. The holes on the mixing apparatus are usually arranged such that the ammonia is injected into the flue gas towards a catalyst bed located downstream in the treatment system.
Ammonia is commonly injected through the mixing apparatus into the flow of flue gas by utilizing an external ammonia vaporization system wherein liquid ammonia, either in an anhydrous or aqueous state, is vaporized in a heater or vaporizer, mixed with dilution air, and then routed to the mixing apparatus for injection into the flow of flue gas at a location upstream of the mixing apparatus. Typically, the ammonia is diluted with water prior to being injected through the mixing apparatus into the flow of flue gas.
To increase the mixing efficiency, some mixing apparatus include baffles disposed adjacent to the holes of the pipes or baffles installed between the pipes. Known mixing apparatus commonly utilize horizontal baffles for creating a turbulent mixing effect. Other mixing apparatus utilize square pipes rather than conventional circular pipes. Other known apparatus utilize baffles located in an upstream position from the pipes to create a wake downstream to increase the ammonia flue gas mixing efficiency.
It is therefore desirable to provide a mixing apparatus that evenly distributes the ammonia into the flue gas before reaching downstream catalyst for heat recovery, steam generation systems, packaged boilers, simple or combined cycle catalyst systems, and fired heaters.