High Temperature Separation Processes

Separating particles from the air at high temperature serves multiple needs that go from thermal energy recovery in several industries to improving the economics of power and incineration plants. 

 

Energy Recovery

Given the difficulty in achieving results by increasing revenues, companies are turning more and more to cutting costs. Reducing energy consumption has become the target for many companies.
 
In sectors such as the cement, particleboard, and pulp & paper, among others, energy is demanded mostly in the form of heat, but frequently most of it is lost throughout the manufacturing process or directly to the stack.

In the cement industry, most plants cool the exhaust stream of the pre-heater tower from 400°C down to 120°C, so it can be cleaned in bag filters, dissipating all that heat into the atmosphere. An increasing number of plants is finding ways to recover that heat which implies to clean the gases.
 
In the panel board industry, many factories cannot run at full capacity due to glowing particles carry over to downstream equipment, such as direct heated dryers (particle board), which can cause fires. In other cases, a second stage dedusting is needed to further reduce ash that can deposit in the panelboards (MDF). For large boilers in the pulp & paper industry, pre-separators are frequently needed to protect bag filters downstream.
 
Client's needs include a highly efficient dedusting system to reduce particles to a level that the exhaust stream can be used for energy recovery purposes and enabling the dryers or bag houses to operate without fire risks. The separator needs to be robust enough to operate at high temperatures with low maintenance/operating costs.
 
ACS solutions include hot cyclones to be placed immediately after the furnaces and high efficiency cyclones as an alternative to ceramic filters for high efficiency separation.
 

Improving the Economics of Powerplants

In waste to energy incinerators (MSW and RDF), among other large boilers, the ash in the flue gas can be captured in a cyclone pre-separator before going into the economizer, followed by hydrate lime (Ca(OH)₂), calcium oxide (CaO) or sodium bicarbonate injection to neutralize acidic gases such as SOx, after which a bag filter is used to comply with emissions standards.
 
The cost for the hazardous ash disposal captured in the bag filter is usually nearly 4 times higher than the disposal of ash captured in the pre-separator. The trigger for the fly ash to be considered “hazardous” lies frequently in its high PH due to the hydraulic lime injection. Whereas it reduces HCL and SOX in the flue gases, it is responsible to turn the fly ash alkaline. When the lime reacts with these gases, it forms a solid byproduct know as “lime ash”. This ash contains not only the unreacted lime, but also the pollutants that were captured during the process, such as heavy metals, like lead, mercury.
 
The next scheme exemplifies the amount of dust collected before (via cyclones) and after hydrated lime injection with a very relevant economic impact. More info in this article. Client's needs include a compact dedusting system, operating with low pressure drop, but efficient enough to capture most of the ash, reducing the amount carried over to the bag filter and which will be much more expensive to handle.
 
ACS solutions include compact and low pressure drop cyclones to be placed immediately after the furnaces and providing a very good compromise between efficiency and cost.