Haldor Topsoe Process Flow Sheet: Manufacture Of Ammonia

Haldor Topsoe Process Flow Sheet of Ammonia Production

HALDOR-TOPSOE PROCESS:

This process departs from Haber’s process. In this process, the residual gas is wasted in the atmosphere.

The advantages of this process are:
1. Greater compactness, and simplicity in the case of converter design since under high-pressure gases have a smaller volume.
2. Elimination of expensive heat exchangers required in processes operated at low pressure.
3. Removal of ammonia with water cooling alone.

Against these are the disadvantages:
1. Shorter life of converters.
2. High apparatus upkeep in the high-pressure operation.
3. Efficiency loss in approximately 20% of making up gas, which is unconverted.

In comparison, the Haldor Topsoe process operates at pressures lower than the Claude process and against the disadvantage of using a heat exchanger for heat recovery and less compactness in converter design. Recovery of 20% of unconverted gas and recycling it to increase the efficiency and conversion of the complete process and the large and massive compressors which are used in Claude process are required to maintain 900 atm which cost millions of  Dollars are avoided in Haldor Topsoe and is thus more economical and good, especially for large capacity process. Also, the life of the converter is very long and ammonia is removed by water-cooling and by knock out the drum.

Process important sections:

1. Naphtha Gas Supply
2. Desulphurization Section
3. Reforming Section
4. CO Conversion Section
5. CO2 Conversion Section
6. Methanation
7. Ammonia Synthesis Section
8. Refrigeration Section
9. Ammonia Absorption Section

AMMONIA SYNTHESIS
CONVERTER

The Haldor Topsoe Process for Ammonia Synthesis

Overview

The Haldor Topsoe process for ammonia synthesis from naphtha is a complex and highly integrated system designed for efficient and economical ammonia production.

Step 1: Naphtha Gas Supply

The process begins with a naphtha feedstock, a mixture of hydrocarbons. This naphtha is the source of hydrogen for the eventual ammonia synthesis.

Step 2: Desulphurization Section

The naphtha stream first encounters a hydrodesulfurization (HDS) unit. Here, sulfur compounds, which are detrimental to the downstream catalysts, are converted to hydrogen sulfide (H2S) by reaction with hydrogen. The H2S is then removed, typically using an amine absorption process.

Removal of Sulfur Compounds

This purification step is crucial to protect the catalysts in the subsequent stages.

Step 3: Pre-Reforming Section (Optional)

Sometimes, a pre-reformer is used before the main reformer. This unit operates at milder conditions and converts the heavier hydrocarbons in the naphtha into simpler, more readily reformable compounds.

Step 4: Reforming Section

The heart of the hydrogen generation process is the reformer. Here, the naphtha reacts with steam over a catalyst (typically nickel-based) at high temperature and pressure.

Steam Reforming Process

This process converts the hydrocarbons into synthesis gas, a mixture primarily of hydrogen (H2), carbon monoxide (CO), and carbon dioxide (CO2).

Step 5: Secondary Reforming (with Air Injection)

The synthesis gas from the primary reformer enters a secondary reformer. In this stage, air is injected. The oxygen in the air reacts with the remaining hydrocarbons and some of the CO, further increasing the hydrogen content and generating the necessary nitrogen for ammonia synthesis.

Step 6: Shift Conversion (High and Low Temperature)

The gas stream from the secondary reformer contains a significant amount of CO. This CO is converted to CO2 and more hydrogen via the water-gas shift reaction.

High-Temperature Shift (HTS)

This is typically done using an iron-based catalyst.

Low-Temperature Shift (LTS)

This is typically done using a copper-based catalyst for higher conversion.

Step 7: CO2 Removal

The CO2 produced in the shift conversion needs to be removed as it's not required for ammonia synthesis and can poison the ammonia synthesis catalyst.

Step 8: Methanation

Trace amounts of CO and CO2 that remain after the CO2 removal stage are converted to methane (CH4) in the methanator.

Step 9: Drying

The purified synthesis gas, now consisting primarily of H2 and N2 in a roughly 3:1 ratio, along with some methane, is dried to remove any remaining water vapor.

Step 10: Ammonia Synthesis Section

The dried and purified synthesis gas enters the ammonia synthesis loop. Here, the key reaction takes place: nitrogen and hydrogen combine over an iron-based catalyst at high pressure and moderate temperature to produce ammonia (NH3).

Step 11: Refrigeration Section

The ammonia leaving the reactor is mixed with unreacted synthesis gas. The mixture is cooled, and the ammonia is condensed and separated.

Step 12: Ammonia Absorption Section (Purge Gas Treatment)

A purge stream containing excess inert gases (like argon and methane) is removed from the synthesis loop to maintain the optimal gas composition.

Step 13: Recycle

Unreacted synthesis gas (H2 and N2) from the ammonia synthesis loop is recycled back to the reactor along with fresh synthesis gas.