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EP-4499573-B1 - METHODS FOR THE PRODUCTION OF SULFATE SALTS AND FURNACE SUITABLE FOR USE IN THESE METHODS

EP4499573B1EP 4499573 B1EP4499573 B1EP 4499573B1EP-4499573-B1

Inventors

  • BLOCK, Christophe
  • LANDUYT, PETER
  • BELMANS, MARC

Dates

Publication Date
20260506
Application Date
20230324

Claims (15)

  1. A furnace suitable for the production of an alkali metal sulfate and/or an alkaline earth metal sulfate from sulfuric acid and an alkali metal chloride and/or an alkaline earth metal chloride, the furnace comprising a first reaction chamber delimited by a bottom reactor wall, a top reactor wall opposite to the bottom reactor wall, and one or more side reactor walls, wherein the furnace comprises one or more electrical resistors placed in a second buffer chamber adjacent to the reaction chamber, wherein the buffer chamber is a closed space delimited by one or more buffer chamber walls, wherein at least one buffer chamber wall is a reactor wall, preferably the top reactor wall, wherein the one or more electrical resistors are placed at a distance from all of the reactor walls such that there is no direct contact between the electrical resistor and the reactor walls, and wherein the one or more electrical resistors are placed such that the electrical resistors can heat the exterior surface of one or more reactor walls by radiation, preferably wherein the one or more electrical resistors are placed at a distance within the range of 1 to 500 mm from the top reactor wall, more preferably within the range of 15-200 mm.
  2. The furnace of claim 1, comprising at least 3 electrical resistors, preferably at least 10 electrical resistors, more preferably at least 25 electrical resistors, most preferably at least 30 electrical resistors.
  3. The furnace of claim 2, wherein the electrical resistors are grouped into at least 2 subgroups, preferably at least 3 subgroups, wherein the subgroups are non-overlapping and the furnace further comprises one or more controllers provided for independently controlling the power supply to each subgroup, and, preferably wherein the controllers are configured to control the power supply such that the power supply to a first electrical resistor in a first subgroup is different from the power supply to a second electrical resistor in a second subgroup.
  4. The furnace of claim 3, wherein the controllers are configured to control the power supply such that the power supply to a first electrical resistor in a first subgroup is different from the power supply to a second electrical resistor in a second subgroup, and preferably wherein the controllers are configured to control the power supply such that the power supply to the first electrical resistor is larger than the power supply to the second electrical resistor, and wherein the number of other electrical resistors located in a sphere of radius R centered on the first electrical resistor is lower than the number of other electrical resistors located in a sphere of radius R centered on the second electrical resistor,
  5. The furnace of claim 4, wherein the furnace comprises at least 10 electrical resistors, preferably at least 25 electrical resistors, more preferably at least 30 electrical resistors, wherein the first electrical resistor is closer to the center of the interior surface of the bottom reactor wall than the second electrical resistor, preferably wherein at least part, and more preferably all of the electrical resistors are arranged into 2 or more concentric circles, and wherein the first electrical resistor is part of a different concentric circle than the second electrical resistor.
  6. The furnace of claim 5, wherein the reaction chamber is configured to receive the reagents near the center of the interior surface of the bottom reactor wall, for example within 0.3D of the center of the interior surface of the bottom reactor wall, wherein D is the largest dimension of the interior surface of the bottom reactor wall, and wherein the furnace is configured to gradually migrate the reaction mixture from the center of the interior surface of the bottom reactor wall to the periphery of the interior surface of the bottom reactor wall, for example by rotating rabble arms, and wherein the controllers are configured to control the power supply such that during operation: the temperature of the reaction mixture located on the interior surface of the bottom reactor wall is substantially constant throughout the reactor; the temperature of the reaction mixture located on the interior surface of the bottom reactor wall increases from the center of the interior surface of the bottom reactor wall to the periphery of the interior surface of the bottom reactor wall, preferably increases by at least 50°C, more preferably increases by at least 100°C; or the temperature of the reaction mixture located on the interior surface of the bottom reactor wall decreases from the center of the interior surface of the bottom reactor wall to the periphery of the interior surface of the bottom reactor wall, preferably decreases by at least 50°C, more preferably decreases by at least 100°C.
  7. A method for the production of an alkali metal sulfate and/or an alkaline earth metal sulfate comprising the steps of: (i) providing sulfuric acid; (ii) providing an alkali metal chloride and/or an alkaline earth metal chloride, preferably an alkali metal chloride; (iii) reacting the sulfuric acid of step (i) with the alkali metal chloride and/or alkaline earth metal chloride of step (ii) under conditions suitable for at least partially converting the sulfuric acid to alkali metal bisulfate and/or alkaline earth metal bisulfate; (iv) reacting the alkali metal bisulfate and/or alkaline earth metal bisulfate of step (iii) under conditions suitable for at least partially converting the bisulfate to sulfate, said conditions comprising heating the reaction mixture; wherein step (iv) is performed in a furnace having a first reaction chamber delimited by one or more reactor walls, each reactor wall having an interior surface facing the first reaction chamber, and an exterior surface opposite to the interior surface; wherein a major amount of the heat supplied to the reaction mixture of step (iv) originates from one or more electrical resistors which heat the reaction mixture and/or from one or more electrical resistors which heat one or more reactor walls, preferably wherein a major amount of the heat supplied to the reaction mixture of step (iv) originates from one or more electrical resistors which radiate the reaction mixture and/or from one or more electrical resistors which radiate the exterior of one or more reactor walls; more preferably wherein at least part, even more preferably all of the one or more electrical resistors are placed at a distance from all of the reactor walls such that there is no direct contact between the electrical resistor and the reactor walls; and, most preferably all of the one or more electrical resistors are placed outside the reaction chamber and radiate the exterior surface of one or more reactor walls.,
  8. The method of claim 7, wherein the first reaction chamber is delimited by a bottom reactor wall, a top reactor wall opposite to the bottom reactor wall, and one or more side reactor walls, and at least part, preferably all of the one or more electrical resistors are placed at a distance within the range of 1 to 500 mm from the top reactor wall, preferably within the range of 15-200 mm; more preferably wherein the electrical resistors placed outside the reaction chamber are located in a second buffer chamber adjacent to the reaction chamber, wherein the buffer chamber is a closed space delimited by one or more buffer chamber walls and wherein at least one buffer chamber wall is the top reactor wall; even more preferably wherein the pressure inside the buffer chamber is higher than the pressure in the reaction chamber and the gas in the buffer chamber is regularly or continuously purged such that HCl concentration in the buffer chamber is maintained below a predetermined level; and, most preferably wherein the heat supplied to the reaction mixture of step (iv) originates from at least 3 electrical resistors, preferably at least 10 electrical resistors, more preferably at least 25 electrical resistors, most preferably at least 30 electrical resistors.
  9. The method of claim 8, wherein the electrical resistors are grouped into at least 2 subgroups, preferably at least 3 subgroups, wherein the subgroups are non-overlapping and the furnace further comprises one or more controllers provided for independently controlling the power supply to each subgroup, and, preferably wherein the power supply to a first electrical resistor in a first subgroup is different from the power supply to a second electrical resistor in a second subgroup.
  10. The method of claim 9, wherein the power supply to a first electrical resistor in a first subgroup is different from the power supply to a second electrical resistor in a second subgroup, and preferably wherein the power supply to the first electrical resistor is larger than the power supply to the second electrical resistor, and wherein the number of other electrical resistors located in a sphere of radius R centered on the first electrical resistor is lower than the number of other electrical resistors located in a sphere of radius R centered on the second electrical resistor.
  11. The method of claim 10, wherein the furnace comprises at least 10 electrical resistors, more preferably at least 25 electrical resistors, most preferably at least 30 electrical resistors, and wherein the first electrical resistor is closer to the center of the interior surface of the bottom reactor wall than the second electrical resistor, preferably wherein at least part, more preferably all of the electrical resistors are arranged into 2 or more concentric circles, and wherein the first electrical resistor is part of a different concentric circle than the second electrical resistor.
  12. The method of claim 11, wherein the reagents are provided near the center of the interior surface of the bottom reactor wall, for example within 0.3D of the center of the interior surface of the bottom reactor wall, wherein D is the largest dimension of the interior surface of the bottom reactor wall, and wherein the reaction mixture of step (iv) is gradually migrated from the center of the interior surface of the bottom reactor wall to the periphery of the interior surface of the bottom reactor wall, for example by rotating rabble arms, and wherein the power supply to the electrical resistors is controlled such that: a) the temperature of the reaction mixture located on the interior surface of the bottom reactor wall is substantially constant throughout the reactor; b) the temperature of the reaction mixture located on the interior surface of the bottom reactor wall increases from the center of the interior surface of the bottom reactor wall to the periphery of the interior surface of the bottom reactor wall, preferably increases by at least 50°C, more preferably increases by at least 100°C; or c) the temperature of the reaction mixture located on the interior surface of the bottom reactor wall decreases from the center of the interior surface of the bottom reactor wall to the periphery of the interior surface of the bottom reactor wall, preferably decreases by at least 50°C, more preferably decreases by at least 100°C.
  13. A method for the production of an alkali metal sulfate and/or an alkaline earth metal sulfate comprising the steps of: (i) providing sulfuric acid; (ii) providing an alkali metal chloride and/or an alkaline earth metal chloride, preferably an alkali metal chloride; (iii) reacting the sulfuric acid of step (i) with the alkali metal chloride and/or alkaline earth metal chloride of step (ii) under conditions suitable for at least partially converting the sulfuric acid to alkali metal bisulfate and/or alkaline earth metal bisulfate; (iv) reacting the alkali metal bisulfate and/or alkaline earth metal bisulfate of step (iii) under conditions suitable for at least partially converting the bisulfate to sulfate, said conditions comprising heating the reaction mixture; wherein step (iv) is performed in a furnace according to any of claims 1-6; wherein a major amount of the heat supplied to the reaction mixture of step (iv) originates from one or more electrical resistors which heat the reaction mixture and/or from one or more electrical resistors which heat one or more reactor walls.
  14. The use of a furnace for the production of an alkali metal sulfate and/or an alkaline earth metal sulfate from sulfuric acid and an alkali metal chloride and/or an alkaline earth metal chloride, wherein the furnace has a first reaction chamber delimited by one or more reactor walls, each reactor wall having an interior surface facing the first reaction chamber, and an exterior surface opposite to the interior surface; wherein the furnace comprises one or more electrical resistors configured to heat the reaction mixture and/or comprises one or more electrical resistors configured to heat one or more reactor walls, preferably wherein the one or more electrical resistors are configured to heat the reaction mixture and/or the exterior of one or more reactor walls by radiation, more preferably wherein at least part, preferably all of the one or more electrical resistors are placed at a distance from all of the reactor walls such that there is no direct contact between the electrical resistor and the reactor walls, and, most preferably wherein at least part, preferably all of the one or more electrical resistors are placed outside the reaction chamber and radiate the exterior surface of one or more reactor walls.
  15. The use of a furnace according to any one of claims 1-6 for the production of an alkali metal sulfate and/or an alkaline earth metal sulfate from sulfuric acid and an alkali metal chloride and/or an alkaline earth metal chloride, and preferably comprising heating the exterior of one or more reactor walls by radiation from the one or more electrical resistors.

Description

Field of the invention The present invention relates to methods for the production of sulfate salts, in particular potassium sulfate, from sulfuric acid and an alkali metal chloride and/or an alkaline earth metal chloride. The invention further relates to a furnace suitable for use in these methods, and use of the furnace for the production of potassium sulfate, from sulfuric acid and an alkali metal chloride and/or an alkaline earth metal chloride. Background of the invention The Mannheim process is a well-known process for producing sodium sulphate (Na2SO4) or potassium sulphate (K2SO4). Generally, for potassium sulphate production, the process consists of two steps - an exothermic reaction of potassium chloride and sulfuric acid to potassium bisulphate and hydrogen chloride as a by-product, and an endothermic reaction to potassium sulphate and hydrogen chloride. The steps are shown by reaction formula (1) and (2). KCI + H2SO4 → KHSO4 + HCl(1)Exothermic reactionKHSO4 + KCl → K2SO4 + HCl(2)Endothermic reaction Most volumes of sodium or potassium sulphate produced by the Mannheim process today, still follow substantially the same methodology which developed in Germany during the nineteenth century. The reaction is performed in a furnace comprising two parts, a combustion chamber at the top and a reaction chamber underneath, separated by a dome (a so-called "muffle furnace"). An example of a muffle furnace used for the Mannheim process is described in e.g. patent document US4303619. The dome, constructed from refractory material, separates the combustion chamber and the reaction chamber, preventing flue gases from mixing with the pure hydrogen chloride gas generated in the Mannheim process, but allowing heat transfer from the combustion chamber to the reaction chamber. Potassium chloride and concentrated sulfuric acid are added into the reaction chamber through an inlet (usually a vertical feeding pipe running through the combustion chamber) and the reaction mixture is continuously stirred using rotating rabble arms. Sometimes a multiple-story reactor is used. The HCl gas generated during the production process can be recovered as a highly pure and concentrated, useful and sellable acid product. Generally, the potassium sulphate obtained from the Mannheim process has moderate chloride content (2% to about 4% by weight). The use of potassium sulphate with high chloride values has become undesirable for the agriculture. Therefore, most of the available prior art is directed to a great extent to producing a lower chloride product while the energy, cost and/or environmental efficiency of the method i.e. the Mannheim process has been neglected. As indicated in the reaction scheme above, the second step in the reaction is endothermic i.e. heat needs to be foreseen above the reaction chamber. This heat is generally supplied by burning heavy fossil fuel which heats up the combustion chamber by convection and radiation, indirectly heating the reaction chamber by radiation from the refractory dome. The combustion chamber reaches a temperature in the range of from 950°C to 1400°C. Heating by heavy fuel has a number of significant drawbacks. The flue gases from the combustion chamber contain various environmental pollutants which need to be captured and treated, in particular NOx emissions are a concern. Heating by heavy fuel is also energy inefficient. Because of the high temperature at which the reaction is run, the Mannheim process uses approximately half a barrel of fuel oil per ton of sulfate. Also, due to the especially high temperature and non-uniform heat transfer, a substantial gradient and locally high temperature spots (hot spots) are formed across the combustion chamber's dome surface. This leads to thermal stress and the corrosive conditions encountered are severe, for instance cracks and tears can form which introduce HCl gas into the combustion gases while additional NOx is being formed at the hot spots. The permeated HCl gas requires that the combustion equipment is coated with heat and corrosion resistant concrete. In the reaction room, parts of the equipment are fabricated of cast ferrous metal construction and are designed with thick cross sections. Despite these measures, a frequent replacement of the metal parts is necessary incurring expenses for e.g. maintenance, replacements cost, lost production time. WO2020/144237A1 describes a method for the production of potassium sulfate in a muffle furnace heated by regenerative burners using natural gas. While this heating method present a significant improvement compared to heavy fuel heated Mannheim processes, it still relies on fossil fuel and has the disadvantage that it does not allow any accurate control of temperature zones. The present inventors have identified a need for improved Mannheim processes employing improved heating methods, e.g. improved heating methods which are more environmentally friendly, do not rely on fossil fuels, and/or allow a