Online Gas Analysis in Ammonia Plants


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Online Gas Analysis in Ammonia Plants - 1

Application Note Online Gas Analysis in Ammonia Plants Application Emerson provides Rosemount Analytical gas analyzer technology for on-line analysis of ammonia plant streams. Strategically placed gas analyzers improve the process efficiency and the purity of the end product. Background Ammonia is used in the production of a variety of products including fertilizer, nitric acid, nylon, pharmaceuticals, and refrigerant. Production of ammonia (NH3) is a two step process. The first step is to produce hydrogen (H2) by reacting natural gas or methane (CH4) with steam in a reformer. The second step is to react hydrogen with nitrogen (N2) in a 3 : 1 ratio over a high-temperature catalyst in the ammonia synthesis process. In the process of reforming natural gas or methane to hydrogen, carbon monoxide (CO) and carbon dioxide (CO2) are formed as by-products. Even at low concen­ rations, both CO and CO2 cause t irreversible problems in the ammonia synthesis process. When the synthesis gas contains CO, a slow permanent deterioration of the catalyst occurs. The presence of CO2 in the synthesis gas can result in the formation of ammonium carbamate, a fine white powder, which precipitates out and causes plugging of the ammonia converter. Therefore, to prevent problems in the ammonia synthesis process and to prolong the life of the expensive catalyst, the removal and measurement of CO and CO2 on a continuous basis is required. Gas Analyzer Applications During the production of ammonia, the gases pass through the steam reformer, high- and low-temperature shift converters, amine scrubber and methanator before entering the ammonia synthesis process. Figure 1 - Gas Analyzer Applications Carbon Dioxide ABSORBENT REGENERATOR AMINE SCRUBBER LOW TEMP. SHIFT CONVERTER HIGH TEMP. SHIFT CONVERTER AMMONIA SYNTHESIS

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Online Gas Analysis in Ammonia Plants - 2

Measuring Point 1: Steam Reformer Natural gas and steam react over catalyst to form H2 and CO: CH4 + H2O Also present is CO2 and unreacted CH4. Reformer efficiency is monitored by measuring unconverted CH4. CO is also measured in preparation for the shift converters. Measuring Points 2A and 2B: High - and Low-Temperature The shift converters remove CO by reacting with steam to form H2 and CO2: CO + H2O The CO content is measured to determine the efficiency of the shift converters. Trace CO and CO2 are measured because they must be removed before the ammonia synthesis process or the CO will...

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