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.

Ammonia production technology

Ammonia production has long been reliant on fossil fuels, with natural gas and naphtha serving as primary feedstocks. However, a paradigm shift is underway, as innovators turn to water as a sustainable source of hydrogen. This revolutionary approach not only reduces dependence on finite resources but also significantly decreases the carbon footprint of ammonia production.

At the heart of this transformation lies the reforming section, where high molecular weight feedstocks are converted into hydrogen, a crucial element in the ammonia synthesis reaction. To achieve the requisite stoichiometric ratio of 3:1 (hydrogen to nitrogen), the feedstock undergoes vaporization and purification before being mixed with steam.

The reforming process itself is a complex, three-step sequence of chemical reactions. First, the feedstock-steam mixture is heated, triggering the decomposition of hydrocarbons into hydrogen, carbon dioxide, and carbon monoxide.
CₙHₘ + H₂O → Cₙ₋₁Hₘ₋₂ + CO + 2H₂ + heat
[CH₄ + H₂O ⇌ CO + 3H₂ + heat] 

Next, the resulting gas mixture undergoes a water-gas shift reaction, where carbon monoxide reacts with steam to produce additional hydrogen and carbon dioxide.

CO + H₂O ⇌ CO₂ + H₂ + heat

Finally, the gas mixture is subjected to an ammonia synthesis reaction, where nitrogen and hydrogen combine to form ammonia. This intricate process is a testament to human ingenuity and the relentless pursuit of sustainability. As the world continues to grapple with the challenges of climate change, the shift towards water-based hydrogen production in ammonia manufacturing represents a significant step forward. By embracing this innovative approach, we can reduce our reliance on fossil fuels, decrease greenhouse gas emissions, and create a more environmentally conscious future.

Primary Reformer 

The ammonia production process relies on a series of carefully designed reactions, each facilitated by specialized equipment. The journey begins in the pre-reformer, where a packed bed of catalyst converts higher-weight hydrocarbons into methane.

Next, the methane is fed into the primary reformer, a tubular reactor housed within an induced draught box heater. Here, an endothermic reaction occurs, fueled by high temperatures (490-600°C) and a carefully selected catalyst. The resulting gas mixture contains approximately 12 mole % methane.

The secondary reformer further refines this mixture, reducing methane content to 0.6 mole % through a combustion process. Pressurized air is introduced, allowing CO and methane to react, ultimately yielding the ideal ratio of nitrogen to hydrogen.

Unconverted carbon monoxide is then addressed through a shift reaction, an exothermic process occurring in both high-temperature and low-temperature shift reactors.

The subsequent purification section employs a gas scrubbing solution (GV) to remove carbon dioxide and carbon monoxide. Remaining impurities are converted to methane in the methanator.

Finally, the purified synthesis gas, boasting the perfect hydrogen-to-nitrogen ratio, is fed into the horizontal ammonia synthesis reactor. Here, a catalytic reaction gives rise to ammonia, marking the culmination of this intricate process.

Block Diagram of Ammonia Process Plant

Decoding Ammonia Synthesis: A Process Flow Diagram Guide for Engineers

Ammonia (NH3) is a foundational chemical building block, critical for fertilizers, plastics, refrigerants, and numerous other industrial applications. Its production is a large-scale, energy-intensive process. A common ammonia synthesis process flow diagram (PFD) employing a liquefaction system for ammonia recovery is shown below. We'll go beyond the typical textbook description, focusing on the why behind the design choices and addressing frequently unanswered questions about process optimization and alternatives.

Ammonia synthesis process flowsheet with liquefaction system

Process Overview:

The diagram illustrates a modified Haber-Bosch process. The core principle is the direct combination of nitrogen (N2) and hydrogen (H2) gases:

N2(g) + 3H2(g) ⇌ 2NH3(g) + Heat

This reaction is exothermic (releases heat) and reversible. High pressure and moderate temperature favor ammonia formation. The liquefaction system serves to recover ammonia from the reactor effluent, increasing overall process efficiency.

Equipment Breakdown & Operational Details:

Equipment	Function	Operation	Unanswered Question Addressed	Unique Angle	Tools
Start-Up Heater	Warms the synthesis gas mixture (N2 + H2) to the initial reaction temperature.	Provides initial energy input for catalyst activation.	Why a start-up heater when the reaction is exothermic?	Alternative start-up methods, such as induction heating of the reactor shell.	Heat Transfer Calculator, Energy Efficiency Analyzer
Reactor	Primary ammonia synthesis takes place.	High pressure (140 kg/cm²) and moderate temperature (250°C at the inlet).	Why not much higher pressure?	Fluidized bed reactor for better heat transfer and temperature control.	Reactor Design Simulator, Process Optimization Software
Waste Heat Boiler	Recovers heat from the hot reactor effluent (440°C).	Generates high-pressure steam.	How to optimize heat recovery?	Explore alternative heat recovery methods, such as organic Rankine cycles.	Heat Exchanger Designer, Thermodynamic Modeling Software
Boiler Feed Water and Reactor Feed Heaters	Preheat the reactor feed using the heat recovered.	Heat Exchangers	What type of heat exchanger is most suitable?	Compare shell and tube and plate-type heat exchangers.	Heat Exchanger Selector, Energy Efficiency Calculator
Water Cooler	Cooling the recycled gas	Plate-type heat exchanger	How to minimize cooling water consumption?	Alternative cooling methods, such as air-cooled heat exchangers.	Cooling System Designer, Water Conservation Analyzer
Recirculation Compressor	Compresses the unreacted N2 and H2 from the separator for recycling to the reactor.	Centrifugal compressor	Why not use a single, larger compressor?	Use a variable speed drive on the compressor to minimize power usage.	Compressor Selection Software, Energy Efficiency Calculator
Cold Heat Exchanger & Ammonia Chiller	Cools the reactor effluent to condense ammonia.	Multi-stage cooling	How to optimize cooling temperatures and flow rates?	Cooling methods, such as liquid nitrogen or liquid air.	Cooling System Designer, Energy Efficiency Calculator
Ammonia Separator	Separates the liquid ammonia from the unreacted N2 and H2 gases.	Flash drum operating at specific temperature and pressure	How to optimize separator design and operation?	Explore alternative separation methods, such as membrane separation.	Separator Design Software, Process Optimization Tool
Let-Down Vessel	Reduce pressure to recycle gas before it flows into the absorber.	Pressure reduction valve	How to minimize pressure drop and energy loss?	Pressure reduction methods, such as expansion valves.	Pressure Reduction Calculator, Energy Efficiency Analyzer
Absorber	Absorb unreacted recycled gas.	Chemical absorption	How to optimize absorber design and operation?	Alternative absorption methods, such as physical absorption.	Absorber Design Software, Process Optimization Tool
Refrigeration Compressor, Accumulator and Flash Vessel	Reduce further gas mixture so the pump can transfer product from the flash vessel	Refrigeration cycle	How to optimize the refrigeration cycle and minimize energy consumption?	Refrigeration methods, such as absorption refrigeration.	Refrigeration Cycle Analyzer

Heat Exchanger: Cooling the liquid product
Ammonia Pump: Transfer Ammonia product to storage

Interactive Tool:

Ammonia Synthesis Material Balance

N2 in Feed (mol/hr):
H2 in Feed (mol/hr):
Reactor Conversion (%):

Results:

Ammonia Produced:

Unreacted N2:

Unreacted H2:

Equipment Sizing Estimator

Feed Flow Rate (kg/hr):
Operating Pressure (bar):

Estimates:

Reactor Volume:

Compressor Power:

Heat Exchanger Area:

Ammonia production by Haber-Bosch process:

Haber Bosch Ammonia production Flowsheet

The Haber-Bosch process, developed in 1913, was a groundbreaking method for large-scale ammonia production. Initially, the process utilized coke oven gas, a byproduct of coal coking, as its primary feedstock. The coke, rich in carbon and hydrogen, was gasified to produce a mixture of carbon dioxide, carbon monoxide, and hydrogen-rich gas. To purify the gas, carbon dioxide was scrubbed out, and the remaining carbon monoxide was removed using an ammoniacal cuprous solution in the scrubber. This yielded a water gas rich in hydrogen. The reaction mixture, comprising nitrogen and hydrogen, was then fed into the synthesis loop. However, this 1913-based design has become less economical in recent times. The shift conversion of CO and CO2 requires larger facilities and operating equipment for water gas, making the process less efficient and more costly. As a result, more modern and efficient methods have been developed to replace this outdated design.

The Haber-Bosch Process Steps

1. Ammonia Production,  The water gas generator produces water gas from coke using high-pressure air and steam. The resulting gas mixture, containing CO, CO2, N2, and H2, is then cooled and scrubbed to remove dust particles.
2. Gasholders ensure a continuous supply of gas and collect residual liquids and condensed particles for drainage.
3. In the shift reactor, carbon monoxide is converted to carbon dioxide and hydrogen by reacting with steam over a catalyst.
4. The gas mixture is then compressed and sent to the carbon dioxide purifier for removal of the CO2 fraction.
5. In the ammonia converter, a packed bed of catalyst converts the synthesis gas into ammonia gas. The product mixture is then fed to the ammonia absorber, where water is added from the top of the column.
6. The resulting ammonia water is cooled by the water cooler and stored. Unreacted gas is recirculated to achieve high conversion rates.

Haber-Bosch Process Conditions in the Converter: 

• Pressure: 330 atm
• Temperature: 500-550°C
• Conversion: 10-30%

Bridging to Emerging Technologies:

• Hybrid Approaches: Combining Haber-Bosch with emerging technologies can be a stepping stone towards more sustainable ammonia production. For example, using renewable energy to produce hydrogen for the Haber-Bosch process can reduce reliance on fossil fuels.
• Modularization: Developing smaller, modular Haber-Bosch units can be more suitable for integration with distributed renewable energy sources and can also be used for on-site ammonia production, reducing transportation costs.
• Gradual Transition: Instead of completely replacing Haber-Bosch, a gradual transition by incorporating elements of emerging technologies can be a more practical approach. This could involve using advanced catalysts developed for electrochemical synthesis in Haber-Bosch plants or adapting existing plants to utilize hydrogen from green sources.

Modifications and Upgrades: Project Ideas 

• Ammonia Separation: Improving the efficiency of ammonia separation from the reactor effluent can reduce energy consumption and improve overall process efficiency. Techniques like absorption or membrane separation can be explored.
• Hydrogen Production: Exploring more sustainable hydrogen production methods, such as electrolysis powered by renewable energy or biomass gasification, can reduce the reliance on fossil fuels for hydrogen feedstock.
• Waste Heat Utilization: Recovering and utilizing waste heat from the Haber-Bosch process can improve energy efficiency and reduce overall energy demand.

Block diagram of ammonia production and Process description, comparision of different ammonia production methods

Naphtha obtained from the distillation of petroleum crude is used as the source of hydrogen which acts as the reactant for the production of ammonia. One mole of Ammonia requires one mole of nitrogen and three moles of hydrogen as per the stoichiometry equation. Natural gas is the better option for hydrogen sources and has advantages over the naphtha process as most of the unit operations are reduced getting down the installation and production costs.

 Block diagram of Ammonia Production Process from Naphtha

Many variations of Haber’s process are now being used for the manufacture of synthetic ammonia some varying to such an extent that they are identified by a name often that of the group of men developing them. Important among these are the modified Haber Bosch, Haldor Topsoe, Claude, Casale, Fauser, and Mount Cenis processes.

All of them are fundamentally the same in that nitrogen is fixed with hydrogen as ammonia in the presence of a catalyst but have variations in the construction of equipment their arrangement, the composition of the catalyst, and temperature and pressure used but an ideal process flow sheet becomes the platform for improvement in the process. A simple block diagram shows the Haber’s process

Process description: The ammonia synthesis process is shown by the simple block diagram in a series of steps as follows


1. Naphtha gas supply: Naphtha is used as feedstock and fuel for the Ammonia plant and is supplied at the offsite Gas Metering station at a pressure of 44kg/cm2g. After metering offsite, the naphtha gas for process feed is directly received at the Ammonia plant battery limit at 40kg/cm2g and 40^oC. Fuel gas is used for burners of feedstock preheater, primary Reformer, Auxiliary superheater and start-up heater in Ammonia plant-Feed gas goes to the Desulphurization unit for sulphur removal, if any and is subsequently processed to produce synthesis gas for Ammonia production.

2. Desulphurization: Raw naphtha contains high sulphur which harms the catalyst in the reforming reactor and even consumes hydrogen by undesired side reactions. A packed bed reactor is utilized for the removal of sulphur. Zinc oxide-based bed absorbs the sulphur.

3. Primary reformer: Naphtha contains carbon and hydrogen compounds to separate hydrogen all the carbon is converted to carbon dioxide and hydrogen by means of steam at high temperatures with the presence of the nickel-based catalyst.


4. Secondary reformer: Nitrogen required for the synthesis reaction is obtained from the air so, the carbon dioxide and hydrogen stream is mixed with the air.

5. Shift conversion: carbon monoxide which is formed in the previous process is converted to carbon dioxide by using steam which results in a shift reaction producing hydrogen. High and low-shift reactors are arranged for this conversion process.

6. CO2 removal: All the carbon dioxide produced is removed by the absorption process. Absorption and stripping towers recover most of the gas that is used in urea production.

7. Methanation: The traces of carbon dioxide and carbon monoxide are converted to methane by means of hydrogen on the catalyst like nickel in a methanation reactor. Heat is produced due to the exothermic reaction.
8. Ammonia synthesis reactor: Iron acts as the catalyst at a temperature of 400^oC and pressure of 142kg/cm2g the reaction proceeds for the formation of ammonia.

9. Chilling system: A compression absorption refrigeration system is used for the liquefaction of ammonia. At 1 atm the boiling point of ammonia is -33^oC.

Ammonia synthesis
flow sheet

A Table of Process Design Modifications in Ammonia Production:

Ever-evolving technologies are been adopted by modern industries to improve the conversion rate with efficiency and less energy consumption for the complete process, some of the competitive designed techniques are given and much more are to be introduced. 

 

Process	Pressure, atm	Temperature, 0C	Conversion,%
Mont Cenis	120	400	8-20
Stami Carbon	310	500	10-30
Fauster-Montecatini	220-230	500	10-30
Casale	500-700	500	15-25
Clued	330-630	540-590	15-25
Haber Bosch	330	500-550	10-30
Nitrogen Eng.Corp	200-300	500-550	10-30
Lummus	270-330	500-510	10-25
Kellogg	300-350	---	10-30
Du Pont	900-1000	500-600	40-80

Ammonia Production Technology Selection Tool

Input Parameters

Production Scale: Small (< 10,000 tonnes/year) Medium (10,000-100,000 tonnes/year) Large (> 100,000 tonnes/year) Energy Source Availability: Abundant Renewables Moderate Renewables Limited Renewables Grid Electricity Fossil Fuels Feedstock Availability: Natural Gas Coal Biomass Other Capital Cost Tolerance: Low Medium High Operating Cost Tolerance: Low Medium High Environmental Impact Target: Low Medium High Technological Maturity Preference: Mature Developing Emerging Location Constraints: Remote Urban Industrial Specific Requirements:

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