Ammonia

Ammonia (NH₃) is a colorless gas with a characteristic of pungent odor. It is soluble in water and is produce industrially from nitrogen (N₂) and hydrogen (H₂) by combining N₂ from the atmosphere (containing 79% N₂) with H₂ produced by steam reforming of natural gas in a one to three ratio respectively.  

Process Overview

The ammonia production process consists of six stages:

1. Desulphurisation
2. Reforming
3. Shift Conversion
4. Carbon Dioxide Removal
5. Methanation
6. Ammonia Synthesis

The ammonia production process is briefly described in the flow chart:

The production process starts with feed natural gas and water being purified before use. The natural gas is desulphurised to reduce sulphur content. The natural gas is then compressed and is routed to the steam reformers to create synthesis gas (syngas) which is mixture hydrogen (H₂) and carbon monoxide (CO) in different ratios. Steam reforming transforms methane (CH₄) and steam into hydrogen, carbon monoxide and carbon dioxide (CO₂) via the reactions:

CH₄ + H₂O → CO + 3H₂

CO + H₂O → CO₂ + 3H₂

CH₄ + 1.5O₂ ↔ CO + 2H₂O

 Carbon monoxide poisons the ammonia synthesis catalysts and must thus be removed with steam. In the shift conversion stage, carbon monoxide is first converted it to carbon dioxide, which is readily absorbed and removed.

CO + H₂O → CO₂ + H₂

 To optimize catalyst efficiency in the ammonia synthesis reactor, carbon dioxide must be removed and any residual carbon monoxide. The synthesis gases then pass through an absorber to remove carbon dioxide and any water vapour by using a solvent. The synthesis gas then enter the methanation stage to removal any residual carbon dioxide and carbon monoxide. This is done by converting the gas to methane (CH₄) via exothermic reactions:

CO + 3H₂ → CH₄ + H₂O

CO₂ + H₂ → CO + H₂O

 The gas leaving the methanation stage is dried since no water is allowed to enter the ammonia synthesis reactor because of its adverse effects on the catalyst. The gases are compressed and sent to the high temperature ammonia synthesis reactor to produce ammonia via the reaction:

N₂ + 3H₂ ↔ 2NH₃

The gaseous ammonia is then cooled and refrigerated to liquid ammonia and stored.

Uses of Ammonia

Approximately 80% the ammonia produced in used in the fertilizer industry. Other uses of ammonia are:

• Manufacture of Nitric Acid
• Water and Wastewater Treatment
• Stack emission control systems
• Industrial refrigeration systems
• Rubber industry
• Pulp and paper industry

Trinidad's Ammonia Industry

There are eleven (11) ammonia plants that include two ammonia complexes on the Point Lisas Industrial Estate with a total annual capacity of 5.2 million metric tonnes (MT).

The first complex comprises the two Tringen plants which are joint ventures between the Government and the Norwegian firm Norsk Hydro; and a third ammonia plant, the oldest in the country, which was formerly owned by W.R. Grace and acquired by Norsk Hydro in 1991; it was formally named Hydro-Agri but is now known as Yara Trinidad Limited.

The second fertilizer complex is one of the world’s largest ammonia complexes and is owned by Potash Corporation of Saskatchewan (PCS) and comprises four ammonia plants and one urea plant.

One plant is owned by Pt Lisas Nitrogen Limited (formerly Farmland Misschem) with an annual capacity of 650,000 MT. The technology used is the Haber Process. The shareholders are Terra Industries and KOCH Minerals Services LLC, being equal partners.

Another plant is owned by Caribbean Nitrogen Company Ltd (CNC), with an annual capacity of 650,000 MT. It is owned by a consortium comprising of subsidiary companies of MAN Ferrostaal, PROMAN and KOCH Industries and local company   EOG Resources Trinidad Ltd.

This consortium also owns another plant, the 650,000 MT per annum Nitrogen2000 plant, which commenced production in 2004.

The PCS 04, PLNL, CNC & N2000 plants use the Kellogg Advanced Ammonia Process.

The ammonia plant of the Ammonia-Urea Ammonium Nitrate-Melamine (AUM) complex is the newest addition to the ammonia manufacturing plants. Its production capacity is approximately 650,000 MT per annum and started production in April 2009. The table below shows the start-up date, technology, and annual capacity for each ammonia plant in Trinidad:

Ammonia must be handled with care at all times. A typical Material Safety Data Sheet (MSDS) can be found at the link given below: http://www.jtbaker.com/msds/englishhtml/a5472.htm

Please refer to the link below for a more detailed description of the ammonia process: http://www.potashcorp.com/media/pdf/about/PCS_Trinidad_Fact_Sheet.pdf