Hydrocarbon Feed Purification for Ammonia Plants

By: Gerard B. Hawkins

Managing Director, CEO

Purification

• Need to remove poisons prior to entering downstream catalyst beds, including • Pre reformers • Primary reformers • HTS • LTS

• Note : no Secondary - poisons do not stick as temperature is too high

• Note that methanator is a purification step • Removes CO and CO2 which poisons

synthesis catalyst

Effect of Poisons Reformer catalyst poisoning

• Increased methane slip Low plant efficiency

• Hot tubes Tube life reduction or tube failure

• Carbon formation Increased pressure drop Increased methane slip and hot tubes

LT Shift catalyst poisoning • Reduced life • Premature plant S/D due to high CO slip

and high pressure drop

Poisons Limits • Steam reforming catalyst requirements

• Process gas feed to reformer (dry basis) Sulfur <0.05-0.1 ppm Poison Chlorides <0.05-0.1 ppm Poison As / V / Pb / Hg<5ppb Poison Olefins <1-2 % Carbon

Formation

• LT shift catalyst requirements

• Process gas feed to LT Shift (dry basis)

Sulfur <0.1 ppm Poison

Chlorides < 5 ppb Severe poison

Effect of Chlorides

Most common as HCl or highly mobile ion Remove to less than 5 ppb Accelerates sintering in catalyst metal

crystallites Deactivates reforming catalyst, most lethal

to LT Shift catalyst In process air added to secondary Weakens catalyst

Typical Configuration

Hydrocarbon Feed

Sulfur Removal

Hydrogenation

Typical Configuration Hydrocarbon Feed

Hydrogenation

Sulfur Removal

Chloride Removal

Hydrocarbon Feed

Hydrogenation Chloride Removal

Sulfur Removal

To Reformer