Advances in Ammonia Removal from Hot Coal Gas Page: 4 of 8
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Objectives
The objective of this study is to develop a successful combination of an NH3 decomposition
catalyst with a zinc-based mixed-metal oxide sorbent so that the sorbent-catalyst activity remains
stable for NH3 decomposition in addition to H2S removal under cyclic sulfidation-regeneration
conditions in the temperature range of 500 to 750 C.
Approach
A number of zinc-based sorbents will be prepared in combination with NH3 decomposition
catalysts. The catalyst candidates include Ni, Co, Mo, and W. Sorbent-catalyst formulations will
be screened for NH3 decomposition activity and H2S adsorption reactivity in a fixed-bed reactor
using simulated coal gas at 1 to 20 atm and 500 to 750 'C. One of the superior formulations will
be tested for long-term durability over at least 30 cycles.
Project Description
Experimental
Sorbent-Catalyst Preparation. A highly promising method was recently developed in
cooperation with a commercial catalyst vendor under this project to prepare suitable sorbent-
catalysts. The catalyst vendor provided the required input to keep the preparation procedure on a
commercial track by making sure that the techniques used were scalable. Several sorbent-
catalysts were prepared using this proprietary technique. The following analytical techniques
were used to characterize sorbent-catalysts: (1) X-ray Diffraction (XRD) for the crystalline
phase; (2) the standard BET method for surface area measurement; (3) Hg-porosimetry for pore
volume, bulk density, average pore diameter and pore size distribution determination; and (4)
Atomic Absorption (AA) Spectrometry for elemental composition analysis.
Experimental Setup. The materials prepared were tested in a laboratory-scale, high-pressure
and high-temperature fixed-bed reactor. Briefly, the experimental setup consisted of a gas
delivery system, a fixed-bed reactor, and a gas analysis system. Using the gas delivery system, a
simulated fuel gas of any desired composition could be generated with the help of bottled gases, a
set of mass flow controllers, and a high-pressure syringe pump. Steam was added to the mixed
dry gas by vaporizing liquid water injected into the gas stream at a controlled rate by a high-
pressure syringe pump. NH3 was added to the gas mixture downstream of the generator where
the temperature was high enough to avoid the formation of ammonium carbonates or sulfides.
The reactor was constructed of a 316 stainless steel pipe. Inside the pipe there was a removable
316 stainless steel 1.0 cm I.D. tube with a porous alumina plate at the bottom that acted as a gas
distributor. The inside of the tube was Alon-processed to prevent corrosion of stainless steel by
sulfurous gases in the presence of steam. The pressure inside the reactor was controlled by a back
pressure regulator and measured by an electronic pressure sensor. The thermocouples were
positioned to measure the temperatures of the preheated feed gas, the reactor bed, and the
product gas. The tests with sorbent-catalyst were conducted with a simulated gas containing 10%
H2, 15% CO, 5 mol% C02, 1 mol% H2S, 15 mol% H2O, 0.18% NH3, and balance N2. The outlet
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Jothimurugesan, K. & Gangwal, S. K. Advances in Ammonia Removal from Hot Coal Gas, report, December 31, 1996; Morgantown, West Virginia. (https://digital.library.unt.edu/ark:/67531/metadc686119/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.