Ammonia and Urea Production from Natural Gas: A Process Overview
Natural gas, a rich source of hydrogen and carbon, serves as the primary feedstock for the production of ammonia (NH3) and urea (CO(NH2)2) in the chemical process industry. The process can be represented by a block diagram, illustrating the unit operations involved in the production of these two chemicals.
Process Description
The process consists of two independent sections: Ammonia Production and Urea Production. The Ammonia Section utilizes natural gas and atmospheric air (comprising 79% nitrogen by volume) as feedstocks to produce ammonia. The Urea Section, on the other hand, employs carbon dioxide (CO2) and ammonia (NH3) as reactants to produce urea.
Unit Operations Involved
1. Natural Gas Pre-treatment: Removal of impurities, such as sulfur compounds and water, from the natural gas feedstock.
2. Steam Methane Reforming (SMR): Conversion of natural gas into hydrogen and carbon monoxide through reaction with steam.
3. Air Separation: Separation of atmospheric air into nitrogen and oxygen using cryogenic distillation or pressure swing adsorption.
4. Ammonia Synthesis: Reaction of hydrogen and nitrogen to form ammonia in the presence of a catalyst.
5. Carbon Dioxide Capture: Recovery of CO2 from the flue gas stream or other sources.
6. Urea Synthesis: Reaction of CO2 and NH3 to form urea in the presence of a catalyst.
Block Diagram Representation
A block diagram illustrating the process can be represented as follows:
Natural Gas → Pre-treatment → SMR → Air Separation → Ammonia Synthesis → Ammonia
CO2 Capture → Urea Synthesis → Urea
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Block diagram of Ammonia and Urea production from Natural Gas |
This block diagram highlights the two independent sections of the process, with the Ammonia Section producing ammonia and the Urea Section producing urea using CO2 and NH3 as reactants.
Ammonia and Urea Production Process
Step 1: Hydrogenation
- Hydrogenation of natural gas to convert sulfur compounds into hydrogen sulfide (H2S)
- Reaction: R-SH + H2 → R-H + H2S
Step 2: H2S Removal
- Removal of H2S by adsorption technique using adsorption beds
- H2S is adsorbed onto the surface of the adsorbent material
Step 3: Steam Reforming
- Steam reforming of natural gas to produce methane and hydrogen
- Reaction: CH4 + H2O → CO + 3H2
- All hydrocarbons are cracked to methane and hydrogen
Step 4: Catalytic Combustion
- Combustion of methane and hydrogen on a catalyst bed with compressed air
- Reaction: CH4 + 2O2 → CO2 + 2H2O
- Produces carbon dioxide, carbon monoxide, nitrogen, hydrogen, and steam
Step 5: Water Shift Reaction
- Conversion of carbon monoxide to carbon dioxide and hydrogen
- Reaction: CO + H2O → CO2 + H2
Step 6: CO2 Removal
- Removal of carbon dioxide by absorption using hot potassium carbonate solution (G.V. solution)
- Reaction: CO2 + K2CO3 → KHCO3 + K2CO3
- Leaves the gas with nitrogen and hydrogen
Step 7: Ammonia Synthesis
- Synthesis of ammonia using nitrogen and hydrogen in an ammonia synthesis reactor
- Reaction: N2 + 3H2 → 2NH3
- Iron is used as the catalyst
Step 8: Urea Synthesis
- Synthesis of urea using ammonia and carbon dioxide
- Reaction: 2NH3 + CO2 → (NH2)2CO + H2O
- Ammonia and carbon dioxide are used as raw materials
Flow Sheet of Urea
Snamprogetti-urea-process-description
Haldor-topsoe-process-flow-sheet
Block-diagram-of-ammonia-production
