AUTOMATION PROFILE AMMONIA MANAGEMENT FROM NATURAL GAS.

This column is based on “Ammonia Production from Natural Gas – Cost Analysis,” a report published by Intratec. It can be found at: www.intratec.us/analysis/ammonia-production-cost.
Ammonia (NH3) is among the most important industrial chemicals, produced by reacting nitrogen and hydrogen in a 1:3 stoichiometric ratio. This world-class commodity chemical is used in a myriad of applications, from fertilizers to wood pulping and drugs.
THE PROCESS
The process described in the following paragraphs is similar to the KBR Purifier process, in which ammonia is synthesized following production of synthesis gas (syngas) from natural gas via steam reforming 
1Figure  Process similar to KBR purifier for ammonia production from natural gas
Natural-gas steam reforming. After being compressed and desulfurized, natural gas is mixed with steam for primary steam-reforming reactions. In a tubular fired heater filled with a nickel-based catalyst, the methane is reacted with steam, generating a crude syngas mixture composed mainly of carbon monoxide (CO) and hydrogen (H2). The partially reformed natural gas is fed to the autothermal reformer (ATR), where the remaining methane is converted to CO and H 2. The effluent from the ATR is cooled, generating steam.
Raw syngas purification. The outlet from the ATR is fed to a two-stage, high- and low-temperature reactor, where the bulk of the CO is converted into carbon dioxide (CO2) and H 2. The shifted gas is then cooled in a boiler-feed-water exchanger, generating steam, and a cooling water exchanger, in such a way that water present in the gas condenses and is removed in a knockout drum. The gas stream is sent to the CO 2 absorption unit, which utilizes a methyldiethanolamine (MDEA) wash to remove CO2. The gas stream, free from CO2, is heated and fed to the methanator, where residual carbon oxides are converted to methane in the presence of methanation catalysts. After being cooled and dried in molecular sieves, the syngas is fed to the syngas purifier, composed of a feed-effluent exchanger, a low-speed expander and a rectifying column. In the syngas purifier, excess nitrogen, methane, most of the argon and other impurities are condensed, to be further vaporized and used as fuel.

Ammonia synthesis. The purified syngas is compressed, heated and fed to the ammonia reactor, an intercooled horizontal converter. The cooled reactor outlet is then directed to a multistream heat exchanger that causes the ammonia to condense, using recycled gas and boiling ammonia as refrigerant. Residual gases are recycled to the syngas compressor upstream.

AYSMMONIA PRODUCTION PATHWA
Since it was developed by Fritz Haber and Carl Bosch, the catalytic synthesis of ammonia from nitrogen and hydrogen has not changed significantly. Because of this, most of the different ammonia manufacturing routes are related to different sources of the two elements, especially H2. In this context, two main ammonia production routes are based on steam reforming. Different pathways for ammonia production are presented in Figure 2.

Figure 2. Ammonia production pathways
Figure 2. Ammonia production pathways
ECONOMIC PERFORMANCE
The operating variable costs (raw materials and net utilities cost) estimated for a facility producing ammonia from natural gas operating in the U.S., using data from the second quarter of 2013, would be about $94 per ton of product.

Edited by Scott Jenkins
Editor’s note: The content for this column is supplied by Intratec Solutions LLC (Houston; www.intratec.us) and edited by Chemical Engineering. The analyses and models presented are prepared on the basis of publicly available and non-confidential information. The content represents the opinions of Intratec only. More information about the methodology for preparing analysis can be found, along with terms of use, at www.intratec.us/che.