Continuous Sorbent Reactions in a High-Temperature Fabric Filter Following Convective Pass Ca(OH)2 Injection for SO2 Removal.
A specially designed two-stage reactor was used to study solid sorbent reactions in the filtration stage of a high-temperature fabric which follow convective pass Ca(OH)2 injection. Solid conversions during the progress of the sorbent reactions were thoroughly analyzed. It was found that, unlike the sorbent reactions in the injection stage, which proceed extremely fast with strong carbonation under high temperatures, the subsequent sorbent reactions in the filtration stage are much slower and residual sorbent is mainly utilized in removing sulfur dioxide (SO2). Two major reaction pathways are discovered in the filtration stage. The first route is through the decomposition of residual calcium hydroxide (Ca(OH)2), which is critical in inducing further sorbent reactions when there is sufficient residual sorbent. The second route is the sulfation of the carbonation product, calcium carbonate (CaCO3), which may become the principal reaction to remove SO2 after the residual sorbent is consumed. The con-vective pass and the fabric filter are found to be equally important reaction sites in the combined process of convec-tive pass sorbent injection with high-temperature filtration. The overall SO2 removal efficiency of the system is affected by both the sorbent injection and filtration conditions.
A Two-Stage Reactor for Studying Sorbent Reactivities in Flue Gas Desulfurization Systems Utilizing a Fabric Filter Collector
A two-stage reactor has proven superior in understanding the complex reactions involved in dry gas-solid reactions responsible for flue gas desulfurization in the medium temperature range (425–650°C). Traditionally, experimental approaches have concentrated on either the in-duct reactivity portion of these reactions, or the reaction in the particulate collector, usually a fabric filter (baghouse). From these current studies we have found that sorbent injection conditions upstream of a fabric filter affect the continued reactivity of the sorbent on the filter as well. Considering the sorbent reaction history in its upstream injection zone is therefore important. An integrated two-stage reactor system is described which was designed to simulate the sequential sorbent reactions from the injection zone to the filtration stage. The experimental results for Ca(OH)2 reacting with SO2 in a single-stage fixed-bed reactor system are compared with our results for this reaction where sorbent conversions and surface a...
Using Fuzzy-Delphi technique to determine the concession period in BOT projects
BOT projects are affected by several risks and uncertainties. One of the most important issues in this type of contract is to determine the length of concession period considering these uncertainties. The previous studies have developed several models to determine the concession period. However, the uncertainties are not taking into account in most of the previous works. Moreover, none of the previous researches has the capability to aggregate the opinions of different experts being involved in a project regarding the values of the uncertain input parameters. In this research, a Fuzzy-Delphi technique is implemented to determine the length of concession period considering uncertainties. Using the proposed Fuzzy-Delphi technique, the values of different uncertain factors affecting a BOT project is determined considering opinions of a group of experts. The NPV value is calculated considering the resulted aggregated values of uncertain input parameters. Finally, the concession period is determined using fuzzy approach. A case study is conducted to evaluate the performance of the proposed methodology. It is shown that the concession period is determined more effectively using the proposed approach.