Method for measuring the rate of conversion in a reduction process

Abstract

The present invention relates to method for measuring the rate of conversion in a reduction process, wherein metal oxide containing charge materials, such as iron oxide powder, are contacted with a reduction gas in a reactor and converted into powder comprising iron and an exhaust gas. The present invention also relates to the use of the rate of conversion measured in such reduction process for adjusting operating conditions in the reactor.

Description

[0001]Title: method for measuring the rate of conversion in a reduction process Description: The present invention relates to a method for measuring the rate of conversion in a reduction process. The present invention also relates to the use of the rate of conversion measured in a reduction process for adjusting operating conditions in the reactor. A reduction process, such as an iron oxide powder reduction process, is known from WO 2023 / 121465 in the name of the present applicants. According to such method the metal oxide containing charge materials is fed to a fluidized bed unit, wherein the metal oxide containing charge materials is reduced by flowing a reduction gas through the fluidized bed unit, wherein the fluidized bed unit is operated under specific reduction conditions. Partially spent reduction gas is removed from the fluidized bed unit and admixed with fresh reduction gas and the mixture of partially spent reduction gas and fresh reduction gas is returned to the fluidized bed unit. A stream containing iron fuel is continuously removed from the fluidized bed unit. Other processes for reducing metal oxide containing charge materials are known from, inter alia, US 2016 / 348199, US 4,082,545, US 3,288,590, US 4,420,332, WO 00 / 01856, and US 3,303,017. US 5,366,897 discloses a process for converting iron-containing feed to a product comprising iron carbide, the process comprising the steps of inputting to a reactor an iron-containing reactor feed; contacting said reactor feed in said reactor with a gas mixture comprising a reducing gas and a carburizing gas; evaluating whether the rate of conversion of reactor feed into iron carbide is acceptable; and adjusting as necessary reactor pressure to convert reactor feed into iron carbide at an acceptable rate; and converting at least a portion of said reactor feed to iron carbide at an acceptable rate. Such process further comprises the steps of generating a phase stability diagram for conditions of temperature, pressure and gas compositions in the reactor, determining from said phase stability diagram whether conditions of temperature, pressure and gas concentrations in the reactor are suitable for converting reactor feed into iron carbide, and adjusting as necessary at least one parameter selected from the group consisting of reactor temperature, reactor pressure, and gas compositions in the reactor to convert reactor feed into iron carbide. US 2022 / 162076 discloses a process comprising a step of providing a biomass feedstock, pyrolyzing the biomass feedstock, thereby generating a biogenic reagent, wherein the biogenic reagent comprises carbon, and a pyrolysis off-gas; optionally, oxidizing the pyrolysis off-gas, thereby generating heat; reacting the biogenic reagent with a selected reactant, thereby generating a reducing gas; optionally, chemically reducing a selected metal oxide in the presence of the reducing gas, thereby generating a reduced form of the selected metal oxide; and recovering the biogenic reagent continuously or periodically, thereby generating a recovered biogenic reagent, wherein the recovered biogenic reagent is activated carbon. In an iron oxide reduction process it is essential to monitor the progress of the conversion process. Possible solutions for monitoring the progress of the conversion process are spectroscopy, such as mass spectrometry (MS) and X-ray fluorescence (XRF), thermogravimetric analysis (TGA), X-ray diffraction (XRD), electrical resistance measurements, microscopy techniques, and load cells, i.e. weight measurements. For example, spectroscopic techniques measure the absorption or scattering of light by the sample, wherein changes in the oxidation state of iron during the conversion process will result in characteristic shifts or peaks in the spectrum, which can be detected and analysed. Some disadvantages of MS include: it takes a long time to obtain results (retention time), the sample will get lost, the technique requires a lot of specialist knowledge, maintenance and calibration and is very expensive compared to others. MS can be applied continuously during operation but only in combination with advanced detectors and fast data processing technologies. TGA measures the change in weight of a sample as it is heated. During the reduction process, the decrease in the sample's weight indicates the conversion of iron oxide to iron. TGA cannot be applied continuously during operation, but it can be performed periodically by taking samples at specific intervals. TGA is suitable for lab-scale reaction kinetics measurements (and therefore conversion) because of its precision and sensitivity to weight changes at varying temperatures. However, it is less suitable at large scale due to the limitations in throughput, scalability and real-time process control that are essential in industrial reactors for optimizing the process with regard to product quality and conversion rate. XRD measures the scattering of X-rays by the sample, wherein the crystal structure of the sample may change during the conversion, resulting in shifts in the XRD pattern that can be identified and analysed. XRD is not suitable for continuous application during operation and needs to be performed periodically by sampling at specific time points. Electrical resistance measurements record the changes in the sample's electrical resistance and, as the conversion progresses, the resistance of the sample changes due to alterations in conductivity. Electrical resistance measurements can generally be performed continuously during operation, allowing for real-time monitoring. Microscopy techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) use imaging to visualize changes in the morphology and structure of the sample. By taking samples at different stages of the conversion process, visible changes in particle size, shape, and composition can be observed. Microscopy requires sample preparation and can be performed periodically by taking samples at specific intervals. By placing the reactor on load cells, changes in the weight of the reactor are detected during the course of the reaction. As the reaction progresses and the conversion of iron oxide to iron powder takes place, the weight of the reactor decreases due to the removal of oxygen from the system. The weight of the reactor can be measured continuously throughout the reaction process. This technique is very difficult because the powder is also continuously dosed and discharged. Actual weight loss due to the reaction is therefore difficult to determine and the fluidized bed causes a lot of vibrations, which is not ideal for load cells. An object of the present invention is to provide a method for measuring the rate of conversion in a reduction process, especially an iron oxide powder reduction process. Another object of the present invention is to use the rate of conversion measured in a reduction process for controlling the reduction process in the reactor, especially in an iron oxide powder reduction process. The present invention thus relates to a method for measuring the rate of conversion in a reduction process, such as an iron oxide powder reduction process, wherein metal oxide containing charge materials, such as iron oxide powder, are contacted with a reduction gas in a reactor and converted into powder comprising iron powder and an exhaust gas, characterized in that the humidity of the exhaust gas is measured and the signal thus measured is used for measuring the rate of conversion. The present inventors found that on basis of measuring the humidity of the exhaust gas in a reduction process, such as an iron oxide powder reduction process the rate of conversion can be determined. The conversion rate is a metric that can be used to indicate the amount of iron oxide powder converted into powder comprising iron. This feature allows the operator to monitor the progress of the conversion process, in real-time, providing valuable information about the efficiency and effectiveness of the reaction. By measuring the conversion rate, one could better understand and optimize the production of powder comprising iron from metal oxide containing charge materials. In addition, the method of measuring the humidity of the exhaust gas in a reduction process, such as an iron oxide powder reduction process can be implemented in small scale laboratory installations, pilot plants and commercial process units as well. The term exhaust gas includes a gaseous stream and can be further processed in downstream units. The present method delivers immediate results and enables real-time monitoring, allowing a process operator to respond immediately to changing conditions. In addition, for applications where a continuous analysis of gas flows is required, the present method provides a continuous monitoring without any interruption of the process. The humidity as mentioned here can be the relative humidity or the absolute humidity. Relative humidity (RH) is a measure of the amount of moisture in a gaseous stream relative to the maximum amount of moisture the gaseous stream can hold at a given temperature. For example a resistor-based hygrometer measures humidity by monitoring the resistance change of a humidity-sensitive material. For calculating the relative humidity accurately a temperature sensor is needed. Absolute humidity is a measure of the actual amount of moisture present in a given volume of a gas. Unlike relative humidity, which is expressed as a percentage and depends on temperature, absolute humidity is an actual measurement of the mass of water vapor in a gas and is not temperature-dependent. In an example of the present method relative humidity is preferred. The term reactor as used here can be a combination of reactors, placed in series or parallel. In addition, the type of reactor can be any type of reactor, such as continuous stirred-tank reactor (CSTR), plug flow reactor (PFR), such as a tubular reactor, fixed-bed reactor, fluidized bed reactor, packed bed reactor, membrane reactor, high-pressure reactor, and trickle bed reactor. The present inventors found that in the method of measuring the humidity of the exhaust gas the conditions during the measurement should be such that occurrence of condensation of the exhaust gas is prevented or reduced to a minimum. In a situation in which condensation of the exhaust gas takes place a correct measurement of the actual humidity of the exhaust gas cannot be carried out since a part of the actual humidity has been transferred from the gaseous phase into the liquid phase. According to an example of the present method a part of the exhaust gas is passed by a humidity sensor which measures the water content in the gas. The water content thus measured is used to determine and monitor the conversion of the iron oxide particles. Such real-time monitoring of the conversion rate enables operators to adjust and to optimize the process, aiming for maximum conversion, efficiency, and powder quality. Furthermore, if the water content in the exhaust gases drops below a certain threshold value, the operator is informed that most iron oxide has reacted towards iron which is a sign that an additional amount of fresh powder must be dosed to the reactor. If the reaction rate decreases one or more process parameters need to be adjusted, such as pressure, temperature and reduction gas flow. In an example the humidity of the reduction gas is measured, and the signal thus measured is considered when measuring the rate of conversion. In an example the mass flow, hydrogen content, temperature and pressure of the reduction gas entering the reactor are measured. In an example of recirculation of process gasses into the reactor, an amount of water in the gas phase may enter the reactor. The purity of gas entering the reactor may not be 100% hydrogen. The amount of such water is measured too. In an example the pressure and temperature of the exhaust gas are measured. In an example the rate of conversion of iron oxide powder towards powder comprising iron is used for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder. In an example of the present method one or more of humidity, pressure and temperature of the exhaust gas, humidity, mass flow, hydrogen content, temperature and pressure of the reduction gas entering the reactor are continuously measured. In an example the reduction gas is a gas comprising hydrogen. In another example the reduction gas further comprises carbon monoxide. Syngas (synthesis gas) is a mixture of hydrogen and carbon monoxide and can be used as a reduction gas. In an example wherein the reduction gas comprises carbon monoxide as well, a sensor for measuring the carbon monoxide content in the reduction gas entering the reactor and a sensor for measuring the carbon dioxide content in the exhaust gas leaving the reactor are needed for accurately measuring the conversion of iron oxide powder towards powder comprising iron. In the reduction reaction carbon monoxide is converted into carbon dioxide via CO + FeO -> CO2+ Fe. The present invention also relates to the use of the rate of conversion measured in a reduction process, such as an iron oxide powder reduction process as discussed above for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder, for controlling the reduction process in the reactor. The present invention also relates to the use of the rate of conversion measured in a reduction process, such as an iron oxide powder reduction process as discussed above for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder, for improving the efficiency of the reduction process in the reactor. The present invention also relates to the use of the rate of conversion measured in a reduction process, such as an iron oxide powder reduction process as discussed above for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder, for improving the quality of the powder comprising iron produced in the reduction process in the reactor. The powder comprising iron thus produced will be used as a fuel in a subsequent process, thus the quality of the powder comprising iron is important. In a situation where the conversion rate is low, the final product will contain unconverted materials, and these unconverted materials will have a negative influence on the subsequent process. The powder possess a good quality when it does not spontaneously self-combust at low temperatures. The present invention also relates to powder comprising iron produced according to a method for measuring the rate of conversion in a reduction process, such as an iron oxide powder reduction process as discussed above, wherein the powder comprising iron has a Sauter mean particle size of at least 10 µm, preferably at least 20 µm, and at most 200 µm, preferably at most 150 µm. The particle size can be measured via laser diffraction. The present invention also relates to the use of powder comprising iron as discussed above in a process for producing high-temperature energy that is converted into one or more of steam, hot air and hot water. The present method focuses on measuring the conversion rate in the reduction process, such as an iron oxide powder reduction process. The conversion rate quantifies the proportion of iron oxide powder converted into powder comprising iron, serving as a key metric for evaluating the reaction process's efficiency and progress. Real-time monitoring of the conversion rate allows operators to optimize the process by timely adjusting operating conditions such as pressure, temperature, or flowrate, aiming to maximize conversion, process efficiency, and powder quality. In addition, changes in exhaust gas water content provide valuable information about the reduction extent and consequently the need for dosing fresh iron oxide powder. Overall, this approach enhances process control, efficiency, and the production of high-quality powder comprising iron. Although the present description focusses on a reduction process, such as an iron oxide powder reduction process, wherein iron oxide powder is contacted with a reduction gas in a reactor and converted into powder comprising iron and an exhaust gas, the present method can also be used for other types of reduction processes, such as processes for manufacturing steel. The present method can be described via the reaction equation of the reduction of iron oxide, wherein iron oxide may be present as a mixture of for example FeO, Fe2O3 and Fe3O4: FeଶOଷ + 3Hଶ ↔ 2Fe + 3HଶOFe3O4 + 4H2 ↔ 3 Fe + 4 H2O FeO + H2 ↔ Fe + H2O Or in more general terms: FexOy + yH2 ↔ xFe + yH2O During the present reduction process, such as an iron oxide powder reduction process, iron oxide powder is contacted with a reduction gas in a reactor and converted into powder comprising iron and an exhaust gas, according to reaction equation. As a result of the reduction reaction, water is formed, the extent of which can subsequently be measured through exhaust gas analysis. Such measurement of the humidity of the exhaust gas can be carried out with a humidity transmitter. This transmitter can be used to determine the volume fraction of water in the exhaust gas. Thereafter, the volume fraction of water in the exhaust gas is used to determine the mass flow of water after the reaction. This flow is then related towards the amount of oxygen (O) that is removed from the iron oxide powder during the reaction. The stoichiometric of the amount of oxygen (O) in the reduction process as discussed here is 1:1. As the initial composition of the powder (FexOy, see above) is known, the conversion is determined via the following formula: Δm X(conversion) = ^,୰^ୟୡ^^^⋅ 100% m^,୧୬୧^୧ୟ୪In a situation where the inlet gas to the reactor is already humid, an additional humidity transmitter positioned upstream of the reactor can be used for making a correction for the actual formed water measured by the humidity transmitter positioned downstream of the reactor. In addition, as the excess hydrogen is recycled to the reactor, a small amount of H2O will enter the reactor since in practice separation of H2O and H2is not 100% perfect and thus a compensation must be carried out, i.e. subtracting that amount from the amount measured at the exhaust. The present method also enables the ability to make conversion plots over time. This data can be utilized to validate reactor models, which can subsequently be employed for optimization of both the reactor and the overall process. A validated reactor model is valuable, since significant optimization steps can be implemented in a new reactor design, e.g. scaling up, reactor geometry, operating conditions, overall mass and energy balance. The invention is further described by reference to a following non-limiting example. In an iron oxide powder reduction process as disclosed in WO 2023 / 121465, wherein iron oxide powder is contacted with a reduction gas in a reactor and converted into powder comprising iron and an exhaust gas, the amount of water (^ு̇మை,^^) in the stream entering the reactor, i.e. the mass flow, is measured, as well as the amount of hydrogen. The amount of water at the outlet of the reactor, i.e. the mass flow, is also measured. On basis of these two measurements the amount of oxygen൫Δ^ை̇,^൯that has reacted in the reactor, i.e. the mass flow, can be calculated, wherein M is the molar mass in kg / mol: Given the initial powder composition (^^௫ ௬^) and the total powder mass flow (^ி̇^^ை^) entering the reactor, the maximum oxygen uptake (Δ^ை̇,^^௫) can be determined: On basis of the measured the amount of oxygen ൫Δ^ை̇,^൯ that has reacted in the reactor and the maximum oxygen uptake ( Δ^ை̇,^^௫) the solids conversion ^ is given by: In the present method for measuring the rate of conversion in a reduction process, such as an iron oxide powder reduction process additional measurements of pressure, temperature and mass flow of the inlet stream of reduction gas in the reactor and the outlet stream of water-containing gas from the reactor are carried out. The values obtained may be used in the calculation of the solids conversion ^. It is to be noted that the present inventors found that in a commercial reduction process more H2is used than theoretically needed to convert all Fe2O3and Fe3O4into Fe. A schematic overview of a reduction process, such as an iron oxide powder reduction process can be found in the enclosed Figure. The iron oxide powder 2 is contacted with a reduction gas 1 in a reactor 5 and converted into powder comprising iron 3 and an exhaust gas 4. The reduction gas 1 entering the reactor 5 is monitored for several process parameters, such as percentage hydrogen 10, percentage humidity 11, temperature 12, pressure 13 and mass flow 14. The exhaust gas 4 leaving the reactor 5 is also monitored for several process parameters, such as percentage humidity 16, temperature 17 and pressure 18. The mass flow of iron oxide powder 2 entering the reactor 5 is measured via a weight transmitter 15 as well. In the Figure separate sensors 10-18 for each process parameters are shown but in practice a sensor can be used for measuring a combination of several parameters. For example, a hydrogen sensor can be used for measuring not only hydrogen but pressure, temperature and humidity as well. Exhaust gas 4 is further processed in downstream equipment (not shown here). An example of process control is as follows. The process operator measures during a steady state situation that the desired conversion rate is not achieved. The process operator may take action to increase the conversion rate. For example, the process operator increases the temperature of the reactor. Such an increase will lead to a faster reaction which is advantageous from both a kinetic and a thermodynamic point of view. For example, the process operator may also increase the pressure of the reactor. Such a higher pressure will result on the one hand in a better mass transfer because the hydrodynamics become better, i.e., smaller gas bubbles, but on the other hand also in a faster reaction due to the higher hydrogen concentration. These two effects are based on different aspects, i.e. the first one is about mass transfer, while the other one is about reaction kinetics. For example, the process operator may also increase the mass flow of the reduction gas. Such an increase may change the fluidization regime in the fluidized bed, e.g. from a bubbling regime to a turbulent regime, resulting in a better mass transfer between gas and iron oxide particle. However, the excess amount of hydrogen will be greater and therefore also the hydrogen recycle (which in turn is less efficient for energy management). A low mass flow of hydrogen is more efficient for the hydrogen conversion and therefore the hydrogen recycling. Such a situation can be seen as an economic consideration where an optimum can be found.

Claims

CLAIMS 1. A method for measuring the rate of conversion in a reduction process, wherein metal oxide containing charge materials, such as iron oxide powder, are contacted with a reduction gas in a reactor and converted into powder comprising iron and an exhaust gas, characterized in that the humidity of the exhaust gas is measured and the signal thus measured is used for measuring the rate of conversion.

2. A method according to claim 1, wherein the humidity of the reduction gas entering the reactor is measured, and the signal thus measured is taken into account when measuring the rate of conversion.

3. A method according to any one or more of the preceding claims, wherein the mass flow, hydrogen content, temperature and pressure of the reduction gas entering the reactor are measured.

4. A method according to any one or more of the preceding claims, wherein the pressure and temperature of the exhaust gas are measured.

5. A method according to any one or more of the preceding claims, wherein one or more of humidity, pressure and temperature of the exhaust gas, humidity, mass flow, hydrogen content, temperature and pressure of the reduction gas entering the reactor are continuously measured.

6. A method according to any one or more of the preceding claims, wherein the reduction gas is a gas comprising hydrogen.

7. A method for measuring the rate of conversion in a reduction process, wherein metal oxide containing charge materials, such as iron oxide powder, are contacted with a reduction gas in a reactor and converted into powder comprising iron and an exhaust gas, characterized in that the reduction gas comprises carbon monoxide, wherein the carbon monoxide content of the reduction gas entering the reactor is measured and the carbon dioxide content of the exhaust gas leaving the reactor is measured, and both signals thus measured are taken into account when measuring the rate of conversion.

8. A method according to claim 7, wherein one or more of carbon dioxide content, mass flow, temperature and pressure of the reduction gas entering the reactor and / or the exhaust gas are measured, preferably on a continuous basis.

9. A method for optimizing a reduction process, such as an iron oxide powder reduction process, wherein the rate of conversion of metal oxide containing charge materials, such as iron oxide powder, towards powder comprising iron is used for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder.

10. The use of the rate of conversion measured in a reduction process, such as an iron oxide powder reduction process, according to any one or more of claims 1-9 for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder, for controlling the reduction process in the reactor.

11. The use of the rate of conversion measured in a reduction process, such as an iron oxide powder reduction process, according to any one or more of claims 1-9 for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder, for improving the efficiency of the reduction process in the reactor.

12. The use of the rate of conversion measured in a reduction process, such as an iron oxide powder reduction process, according to any one or more of claims 1-9 for adjusting operating conditions in the reactor such as pressure, temperature, or flowrate of the reduction gas and iron oxide powder, for improving the quality of the powder comprising iron produced in the reduction process in the reactor.

13. Powder comprising iron produced according to a method for measuring the rate of conversion in a reduction process, such as an iron oxide powder reduction process, according to any one or more of claims 1-9, wherein the powder comprising iron has a Sauter mean particle size of at least 10 µm, preferably at least 20 µm, and at most 200 µm, preferably at most 150 µm.

14. The use of powder comprising iron according to claim 13 in a process for producing high-temperature energy that is converted into one or more of steam, hot air and hot water.

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