Applied Petrochemical Research https://doi.org/10.1007/s13203-018-0222-9
RESEARCH NOTE
Water effect on the new catalyst of high temperature shift conversion during first reduction Mohamed A. Fouad M. Gaber1 Received: 13 October 2018 / Accepted: 16 November 2018 © The Author(s) 2018
Abstract The water–gas shift reaction plays a major role in ammonia and hydrogen plant design and operation. Good performance of the shift catalysts, and attainment of a close approach to equilibrium and, hence, minimization of the CO slip from the catalyst system is critical to the efficient and economic operation of the plant and ensures maximum hydrogen production from the hydrocarbon feedstock. Excessive drying out of catalyst during first reduction was studied to identify its influence on the catalyst during normal operation. Keywords Shift conversion catalyst · Catalyst reduction · Ammonia plant · Hydrogen plant · Water effect
Introduction The water gas shift reaction is an essential step in modern ammonia plants. Efficient and reliable shift conversion is required to ensure that the highest yield of hydrogen can be obtained from the reformed hydrocarbons. Hence, good performance of the shift catalyst and attainment of equilibrium CO slip from the catalyst system is critical for the efficient and economic operation of the plant to maximize the hydrogen production from the plant. In most ammonia plants, the shift conversion is carried out in two stages. Usually, a high temperature shift (HTS) catalyst is used as the first stage and typically converts over 80% of the CO. A low temperature shift catalyst (LTS) then converts the majority of the remaining CO [1]. As well as maximizing the hydrogen production, the water gas shift reaction also maximizes the CO2 production from an ammonia plant. In addition, carbon oxides, both carbon monoxide and carbon dioxide (COx), are a poison to the ammonia synthesis catalyst and, therefore, must be removed. CO is converted into CO2 for easier removal in the CO2 removal system. CO2 is an essential component for the Urea plant [1]. The high temperature shift (HTS) catalyst is comprised of iron oxide, with a chromium oxide stabilizing agent to * Mohamed A. Fouad M. Gaber
[email protected] 1
Chemical Engineering Department, Faculty of Engineering, Alexandria University, P. O. Box 21544, Alexandria, Egypt
reduce the rate of sintering of the active iron crystallites at high temperatures [2]. More recently, copper has been added to the formulation to increase the activity per unit bed volume and to provide protection against catalyst over-reduction at low steam–gas ratios [3]. Typical operating temperatures for a high temperature shift catalyst are between 310 and 460 °C and at this temperature, a new catalyst charge should be able to reduce the CO level at the reactor exit close to the equilibrium level of the process conditions, usually in the range 2–3 mol%. At these temperatures, iron has sufficient activity to deliver the required performance. Virtually, all high temperature shift catalysts are in the form of pellets of Fe2O3/Cr2O3/CuO, with 88%, 9%, and 2.6%, respectively. A small level of residual impurities are from the manufacturing process, primarily sulfur (production specification
