Novel Technologies for Gaseous Contaminants Control

Abstract

The overall objective of this project is to develop technologies for cleaning/conditioning the syngas from an integrated gasification combined cycle (IGCC) system to meet the tolerance limits for contaminants such as H 2 S, COS, NH 3 , HCN, HCl, and alkali for fuel cell and chemical production applications. RTI's approach is to develop a modular system that (1) removes reduced sulfur species to sub-ppm levels using a hybrid process consisting of a polymer membrane and a regenerable ZnO-coated monolith or a mixed metal oxide sorbent; (2) removes hydrogen chloride vapors to sub-ppm levels using an inexpensive, high-surface area material; and (3) removes NH 3 with acidic adsorbents.RTI is working with MEDAL, Inc., and North Carolina State University (NCSU) to develop polymer membrane technology for bulk removal of H 2 S from syngas. These membranes are being engineered to remove the acid gas components (H 2 S, CO 2 , NH 3 , and H 2 O) from syngas by focusing on the "solubility selectivity" of the novel polymer compositions. The desirable components of the syngas (H 2 and CO) are maintained at high-pressure conditions as a non-permeate stream while the impurities are transported across the membrane to the low pressure side. RTI tested commercially available and novel materials from MEDAL using a high-temperature, high-pressure (HTHP) permeation apparatus. H 2 S/H 2 selectivities >30 were achieved, although there was a strong negative dependence with temperature. MEDAL believes that all the polymer compositions tested so far can be prepared as hollow fiber membrane modules using the existing manufacturing technology.For fuel cell and chemical applications, additional sulfur removal (beyond that achievable with the membranes) is required. To overcome limitations of conventional ZnO pellets, RTI is testing a monolith with a thin coating of high surface area zinc-oxide based materials. Alternatively, a regenerable sorbent developed by DOE/NETL (RVS-1) is being evaluated for this application. A multi-cycle test of 2-in. (5-cm) diameter monolith samples demonstrated that <0.5 ppm sulfur can be achieved.Removal of HCl vapors is being accomplished by low-cost materials that combine the known effectiveness of sodium carbonate as an active matrix used with enhanced surface area supports for greater reactivity and capacity at the required operating temperatures. RTI is working with SRI International on this task. Sorbents prepared using diatomaceous earth and sepiolite, impregnated with sodium carbonate achieved steady-state HCl level <100 ppb (target is 10 ppb). Research is continuing to optimize the impregnation and calcination procedures to provide an optimum pore size distribution and other properties.RTI and SRI International have established the feasibility of a process to selectively chemisorb NH 3 from syngas on high surface area molecular sieve adsorbents at high temperatures by conducting a series of temperature-programmed reactions at 225C (437F). Significant levels of NH 3 were adsorbed on highly acidic ads...

Integrated Process Configuration for High-Temperature Sulfur Mitigation during Biomass Conversion via Indirect Gasification

“…Several more recent references cite even lower sulfur tolerances. Boerrigter, et al, (2002) state that sulfur levels in syngas for FTS should be below 1 ppmv and Turk, et al, (2001) claim that the total sulfur content in syngas should be 60 ppb. In general, for a fixed bed reactor design, any catalyst poison will have the most pronounced affect near the gas inlet and propagate through the reactor towards the outlet, whereas in a fluidized bed design the poison will have a uniform affect throughout the reactor.…”

“…Other syngas impurities are also known to poison FTS catalysts. Halide levels in syngas should be less than 10 ppb (Boerrigter, et al, 2002) and referenced nitrogen levels are 10 ppmv NH 3 , 0.1 ppmv NO x and 10 ppb HCN (Turk, et al, 2001). Additionally, water oxidizes FT catalysts (both Fe & Co) but the rate of oxidation is higher for the iron catalyst.…”

“…Table 24 summarizes the syngas impurities and tolerances. Dry, 1981Boerrigter, et al, 2002Turk, et al, 2001 Halides 10 ppb Boerrigter, et al, 2002 Nitrogen 10 ppmv NH3 0.2 ppmv NOx 10 ppb HCN Turk, et al, 2001 Note: There are differing points of view regarding sulfur level but in general, the sulfur content of the syngas should be minimized according to economics.…”

Investigation of competitive COS and HCN hydrolysis reactions upon an industrial catalyst: Langmuir-Hinshelwood kinetics modeling

“…After multiple gas conditioning steps aimed at reaching the required specifications (H 2 /CO ratio adjustment and CO 2 removal) [4,5], the syngas undergoes the Fischer-Tropsch reaction in order to produce synthetic liquid fuel [6][7][8]. However, synthesis gas also contains various impurities that must be removed in order to prevent Fischer-Tropsch catalyst poisoning [9][10][11][12][13]. Integrated Gasification Combined Cycles (IGCC) power generation processes also constitutes more efficient and cleaner alternative technology for future energy production [14][15][16].…”

Partitioning of fuel bound nitrogen in biomass gasification

“…Introduction Nitrogen compounds in biomass-derived syngas are considered minor constituents in terms of their concentrations, but play an outsized role in determining the quality of syngas. Ammonia (NH3) and hydrogen cyanide (HCN) represent NOXprecursors when syngas is burned[20], and they can poison catalysts during chemical synthesis[58].Methods of measuring HCNThe most common method of measuring HCN in syngas is the wet chemical technique, which entails bubbling syngas through a basic solution, usually dilute sodium hydroxide (NaOH). Upon exposure to the base, HCN dissolves into the aqueous phase as cyanide ion (CN -).…”