WO2025067915A1 - Method of maintaining reactant gas pressure in a loop for the preparation of chemical products - Google Patents

Abstract

Method of keeping reactant gas pressure in a loop for the preparation of chemical products prepared by conversion the reactant gas at a constant rate at variating reactant gas supply into a centrifugal compressor equipped with variable pitch of impeller vanes inside the compressor to regulate flow from the compressor into the loop and/ or inside the loop and by adjusting the pitch of the impeller vanes and by keeping the compressor speed nearly constant to obtain the constant pressure rate.

Description

Title: Method of maintaining reactant gas pressure in a loop for the preparation of chemical products

The present invention relates to maintaining the reactant pressure in loops for the preparation of chemical products at fluctuating supply of reactant gas being prepared by means of renewable energy and/or feed stocks.

Large synthesis loops in chemical plants are invariably using centrifugal compressors to obtain the required pressure in the synthesis loop. At reduced capacity, the compressor speed is reduced and thereby the discharge pressure.

A centrifugal compressor is a type of dynamic compressor that utilizes rotating impellers to increase the pressure and flow rate of a gas. It used in various applications such as gas turbines, oil refineries, petrochemical plants, and HVAC systems.

The basic operation of a centrifugal compressor involves the following steps:

1 . Inlet: The gas enters the compressor through the inlet pipe and flows into the impeller eye, which is the central portion of the impeller.

2. Impeller: The impeller consists of a series of rotating blades or vanes. As the impeller rotates, it imparts kinetic energy to the gas, causing it to move radially outward.

3. Diffuser: The diffuser is a stationary component that surrounds the impeller. Its purpose is to convert the kinetic energy of the gas into pressure energy by gradually decelerating the gas and redirecting its flow direction.

4. Outlet: The compressed gas exits the compressor through the outlet pipe at a higher pressure and is then directed to the desired location for further use or processing.

Various design factors, such as impeller diameter, impeller geometry, rotation speed and impeller rotational speed determines the volumetric capacity of the compressor, whereas impeller tip speed and casing diameter is an important parameter for the maximal discharge pressure.

The performance characteristic of a centrifugal compressor is that the volume flow is roughly proportional to the rotation speed while the compression ratio is closer to the rotation speed in the second power.

In traditional applications, when lowering the rotational speed, the discharge pressure will also reduce, but this is often acceptable. However, if the capacity is varying a lot, such as in plants operating on renewable energy, such pressure variations in the long run will cause stress fatigue and risk of rupture of high-pressure equipment.

Pressure variations are prevented by running the compressor at constant or near constant speed. The desired capacity is obtained by routing part of the gas from the discharge side back to the suction. On the other hand, this will substantially increase the specific energy consumption of the synthesis loop when operating at reduced capacity.

In traditional applications, continuous operation at high capacity is the normal philosophy, and since limitations in feedstock are relatively rare and since minor pressure variations are acceptable as per codes for stress fatigue, stress fatigue is generally not considered, so capacity control is performed by adjusting the compressor speed and/or operation of the kickback system. When large and frequent capacity variations are anticipated, such as when operating on renewable energy, where large capacity changes are expected up to several times per day, stress fatigue shall be considered in the mechanical design. This also means that without an adequate pressure control in a loop for the preparation of chemical products energy it will not be possible to revamp existing plans to operate on renewable energy sources.

There are two ways to counter the problem:

One possibility is to reduce the effects of the varying feed by introducing a very large buffer capacity upstream the compressor. This solution has been suggested previously and in principle solves the problem. The downside is that due to large and virtual unpredictable variations in renewable power supply, the required buffer volume will be very large for most applications.

An alternative solution, expected to enable very large capacity variations at constant discharge pressure is to introduce a compressor having impellers provided with variable pitch. Variable pitch is a principle presently not implemented in compressors but has been realized in systems such as ship propellers, wind turbines, large air fans and lately, military aircraft engines.

Variable-pitch compressors provide the ability to adjust the angle of the compressor blades based on the specific requirements of the system. This flexibility allows the compressor to operate efficiently over a wide range of conditions, such as varying gas flow rates, pressure differentials, and rotational speeds.

Thus, the present invention provides a method of maintaining reactant gas pressure in a loop for the preparation of chemical products prepared by conversion of the reactant gas at a constant rate at variating reactant gas into a centrifugal compressor equipped with variable pitch of impeller vanes inside the compressor to regulate flow from the compressor into the loop and/or inside the loop and by adjusting the pitch of the impeller vanes and by keeping the compressor speed nearly constant to obtain the constant pressure rate.

The invention is particularly relevant in the preparation of green synthesis gas. Green synthesis gas is a mixture of carbon monoxide (CO) and/or carbon dioxide (CO2) and hydrogen (H2) gases or nitrogen (N2) and hydrogen (H2) produced from renewable feedstocks using renewable energy, such as wind power and solar power.

While green syngas production offers potential benefits in terms of reduced greenhouse gas emissions and dependence on fossil fuels, there can still be challenges and problems associated with its preparation.

One of the biggest problems for ensuring a consistent and reliable supply of feedstocks is fluctuations in wind and solar power for use in electrolysis of water for the preparation of hydrogen. The invention is preferably employed when the reactant is synthesis gas comprising carbon monoxide (CO) and/or carbon dioxide (CO2) and hydrogen (H2) or nitrogen (N2) and hydrogen (H2) or hydrogen (H2) produced by using renewable energy. Synthesis gas prepared by means of the invention is advantageously utilized in the preparation of green methanol or green ammonia.

In a preferred embodiment of the invention the reactant gas contains hydrogen. In a further embodiment of the invention, the loop is a hydrotreating loop.

Hydrotreating is an important step in refining processes, especially for producing fuels that meet regulatory specifications and environmental standards. In the hydrotreating process, hydrogen gas is mixed with the hydrocarbon feedstock. The presence of hydrogen is crucial for the removal of sulfur, nitrogen, and other impurities.

In many chemical reactions it is necessary to provide constantly a so called make up to compensate for reactant consumption.

Thus, in an embodiment the centrifugal compressor is a make-up gas compressor.

The conversion of chemical reactants is usually limited by the reaction equilibrium making it necessary to recirculate unconverted reactants in the loop back to the chemical reactor.

Thus, in a further embodiment of the invention, the centrifugal compressor is a recirculation compressor.

Claims

Claims

1. Method of maintaining reactant gas pressure in a loop for the preparation of chemical products prepared by conversion of the reactant gas at a constant rate at var- iating reactant gas supply into a centrifugal compressor equipped with variable pitch of impeller vanes inside the compressor to regulate flow from the compressor into the loop and/or inside the loop and by adjusting the pitch of the impeller vanes and by keeping the compressor speed nearly constant to obtain the constant pressure rate.

2. Method of claim 1 , wherein the reactant gas is synthesis gas comprising carbon monoxide (CO) and/or carbon dioxide (CO2) and hydrogen (H2) or nitrogen (N2) and hydrogen (H2) or hydrogen (H2) produced by using renewable energy.

3. Method of claim 1 or 2, wherein the chemical products are green methanol or green ammonia.

4. Method of claim 1 , wherein the reactant gas contains hydrogen.

5. Method of claim 4, wherein the loop is a hydrotreating loop.

6. Method of any one of claims 1 to 5, wherein the centrifugal compressor is a make-up gas compressor.

7. Method of any one of claims 1 to 5, wherein the centrifugal compressor is a recirculation compressor.