PROCESS FOR PRODUCING SYNTHESIS GAS BY GASIFYING SOLID CARBON CARRIERS

Abstract

A process for producing synthesis gas by gasifying a carbon carrier in a slurry having a significant content of phosphorus. According to the invention, the phosphorus compounds dissolved in the liquid phase of the suspension are at least partly precipitated by treating the suspension by increasing the pH of the suspension and/or increasing the concentration of metal cations in the suspension, before the suspension is heated further and subsequently applied to the gasification reactor.

Claims

1-10. (canceled)

11. A process for producing a synthesis gas comprising hydrogen and carbon oxides by gasifying a carbon carrier comprising phosphorus and ash formers, especially solid, phosphorus-containing biomass, comprising the following process steps: (a) providing a suspension (slurry) comprising carbon-containing solids in finely divided form and a liquid dispersant; (b) treating the suspension by increasing the pH of the suspension and/or increasing the concentration of metal cations in the suspension; (c) feeding the treated suspension to a gasification reactor and converting the treated suspension in the gasification reactor under gasification conditions with at least one gasifying agent to give a synthesis gas comprising hydrogen and carbon oxides; (d) discharging the synthesis gas from the gasification reactor and optionally feeding the synthesis gas to further conditioning and/or conversion steps; and (e) discharging a solid or liquid slag from the gasification reactor.

12. The process according to claim 11, wherein in process step (c) the pH is increased to values of at least 7.

13. The process according to claim 11, wherein in process step (c) the pH is increased to values of at least 9.

14. The process according to claim 11, wherein in process step (c) the pH is increased to values of at least 10.

15. The process according to claim 11, wherein in process step (c) the concentration of metal cations in the suspension is increased by adding salts which are at least partly soluble in the dispersant and contain at least one cation selected from the group comprising Ca, Al, Fe.

16. The process according to claim 11, wherein the dispersant contains water.

17. The process according to claim 11, wherein the treated suspension, before being fed to the gasification reactor, is preheated to a temperature of at least 20 C., preferably at least 60 C., most preferably at least 120 C.

18. The process according to claim 11, wherein in process step (c) the pH of the suspension is increased by adding Na.sub.2CO.sub.3 and/or in that a salt which is at least partly soluble in the dispersant and contains Fe is added to the suspension when the slag is to be discharged from the gasification reactor in liquid form.

19. The process according to claim 11, wherein in process step (c) a salt which is at least partly soluble in the dispersant and contains at least one cation selected from the group comprising Ca and Al is added to the suspension when the slag is to be discharged from the gasification reactor in solid form.

20. The process according to claim 11, wherein the solid phosphate precipitates formed in the treatment of the suspension in process step (c) are fed to the gasification reactor together with the suspension.

21. The process according to claim 11, wherein, in a continuous process regime, the suspension is treated in a vessel in process step (c) in such a way that the hydrodynamic residence time T is at least 2 min, preferably at least 5 min, most preferably at least 10 min, the suspension being maintained in the vessel during the residence time by mixing, preferably by stirring.

22. The process according to claim 11, wherein the phosphorus present in the carbon carrier is at least partly in the form of phosphorus compounds that are at least partly soluble in the dispersant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0023] A preferred configuration of the process according to the invention is characterized in that in process step (c) the pH is increased to values of at least 7, preferably at least 9, most preferably at least 10. In principle, the ease with which the phosphates are precipitated, for example as sparingly soluble calcium phosphates, increases with the pH.

[0024] It has been found to be particularly advantageous when, in process step (c), the concentration of metal cations in the suspension is increased by adding salts which are at least partly soluble in the dispersant and contain at least one cation selected from the group comprising Ca, Al, Fe. All these metal cations form sparingly soluble phosphates. If necessary, the solubility of the respective phosphate can be minimized further by additional adjustment of the pH.

[0025] In a preferred manner, the inventive treatment of the slurry in process step (c) is effected at room temperature or at the production or storage temperature of the slurry. It is preferably effected before the temperature of the slurry is increased further, for example prior to addition of the slurry to the gasification reactor.

[0026] It is particularly preferable when an aqueous dispersant is used, for example water, water-containing pyrolysis condensate or water-containing pyrolysis oil. The water content facilitates the production of the slurry and the precipitation of the phosphorus component in insoluble form, and can also serve as a moderator or gasifying agent in the gasification reactor.

[0027] It has been found to be particularly advantageous when, in the process of the invention, the treated suspension, before being fed to the gasification reactor, is preheated to a temperature of at least 20 C., preferably at least 60 C., most preferably at least 120 C. Since the gasification is usually conducted at pressures well above atmospheric pressure, the evaporation of water, for example, out of the slurry is substantially avoided at the temperatures mentioned and, at the same time, the solubility of the phosphates is reduced.

[0028] In a particular configuration of the process according to the invention, in process step (c) the pH of the suspension is increased by adding Na.sub.2CO.sub.3 and/or a salt which is at least partly soluble in the dispersant and contains Fe is added to the suspension. This lowers the melting point of the ash/slag, and allows the slag to be reliably discharged from the gasification reactor in liquid form.

[0029] In an alternative configuration of the process according to the invention, in process step (c) a salt which is at least partly soluble in the dispersant and contains at least one cation selected from the group comprising Ca and Al is added to the suspension. This measure increases the melting point of the ash/slag, and allows the slag to be reliably discharged from the gasification reactor in solid form by means of suitable discharge devices.

[0030] In a preferred configuration of the process according to the invention, the solid phosphate precipitates formed in the treatment of the suspension in process step (c) are fed to the gasification reactor together with the suspension. This dispenses with the complex separation of the phosphate particles from the carbon carrier. The presence of the precipitated phosphates in the slurry does not put its use as feedstock for the gasification reactor at risk, since the solids content additionally generated thereby is small compared to the total solids content in the slurry and this alters the essential rheological and other properties of the slurry only to a very minor degree.

[0031] In a further preferred configuration of the process according to the invention, in a continuous process regime, the treatment of the suspension in process step (c) in a vessel is effected in such a way that the hydrodynamic residence time T is at least 2 min, preferably at least 5 min, most preferably at least 10 min, the suspension being maintained in the vessel during the residence time by mixing, preferably by stirring. Experience shows that, when these residence times are used, reliable precipitation of the phosphates dissolved in the liquid phase of the slurry is possible.

[0032] The process according to the invention can also be conducted batchwise. For this purpose, batches of the slurry are treated by increasing the pH of the suspension and/or increasing the concentration of metal cations in the suspension and subsequently used as gasification feed.

[0033] It is particularly favourable when the phosphorus present in the carbon carrier is at least partly in the form of phosphorus compounds that are at least partly soluble in the dispersant. The greater the solubility of the phosphorus compounds in the dispersant, preferably water, the greater that proportion of phosphorus which can be removed in accordance with the invention prior to the introduction into the gasification reactor.

Working Example and Numerical Example

[0034] Further features, advantages and possible uses of the invention will also be apparent from the description of a working example and numerical example which follows. All the features described alone or in any combination form the subject-matter of the invention, irrespective of their combination in the claims or their dependency references.

Example

[0035] A simplified example is used to represent the procedure according to the notice of invention. For better comprehension, an example highly abstracted in the manner of a model for the two inventive configurations of the process step according to claim 1. (c) is presented. The starting basis considered was merely the liquid phase of an aqueous slurry containing water-dissolved calcium phosphate in the slightly acidic range. What is considered subsequently is the aqueous system containing 1000 g of water with 5 g of calcium phosphate and further calcium ions in the form of 1 g of CaCl.sub.2) and a proton source in the form of 0.1 g of HCl.

[0036] Thermodynamic calculations with the calculation program FactSage showed that, in the course of heatingas also observed in the real casefree phosphate ions are still present in the solution, which precipitate as hydroxylapatite Ca.sub.5(PO.sub.4).sub.3(OH) with free calcium ions when the temperature is increased (Table 1, comparative example).

[0037] In order to prevent this precipitation when the temperature is increased, in accordance with the invention, the pH was raised by addition of 0.55 g of NaOH. As a result, the phosphate was already virtually completely precipitated at room temperature, and no further precipitation of hydroxylapatite occurred with rising temperature (Table 2, invention).

[0038] In an alternative configuration, quicklime (calcium oxide, CaO) was added. Table 3 shows the effect of addition of 0.38 g of CaO. Here too, no further precipitation of hydroxylapatite occurred with rising temperature (Table 3, invention).

INDUSTRIAL APPLICABILITY

[0039] The invention provides an improved gasification process with which it is also possible to utilize slurries produced from phosphorus-containing carbon carriers, especially from corresponding biomass, as feedstocks for the production of synthesis gas. In the gasification process improved in accordance with the invention, there is less frequent occurrence of interruptions to operation that are caused by blockages of conduits, apparatuses and nozzles. The availability of the gasification plant for production operation is increased and hence the economic viability of the gasification process is improved.

[0040] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0041] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0042] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0043] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0044] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0045] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

[0046] All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

TABLE-US-00001 TABLE 1 Precipitated amounts of hydroxylapatite and pH values as a function of temperature for the system 1000 g H.sub.2O + 5 g Ca.sub.3(PO.sub.4).sub.2 + 0.1 g HCl + 1 g CaCl.sub.2 p T Hydroxylapatite (s) (bar) (C.) (g) pH 40 20 4.47 3.45 40 30 4.49 3.34 40 40 4.50 3.25 40 50 4.52 3.15 40 60 4.55 3.07 40 70 4.57 2.99 40 80 4.60 2.91 40 90 4.63 2.84 40 100 4.66 2.78 40 110 4.68 2.71 40 120 4.71 2.66 40 130 4.74 2.60 40 140 4.77 2.55 40 150 4.80 2.51 40 160 4.83 2.46 40 170 4.86 2.42 40 180 4.88 2.38 40 190 4.91 2.35 40 200 4.93 2.32 40 210 4.94 2.31 40 220 4.95 2.29 40 230 4.96 2.29 40 240 4.96 2.29 40 250 4.96 2.29

TABLE-US-00002 TABLE 2 Precipitated amounts of hydroxylapatite and pH values as a function of the temperature for the system 1000 g H.sub.2O + 5 g Ca.sub.3(PO.sub.4).sub.2 + 0.1 g HCl + 1 g CaCl.sub.2, addition of 0.55 g NaOH p T Hydroxylapatite (s) (bar) (C.) (g) pH 40 20 5.40 10.59 40 30 5.40 10.26 40 40 5.40 9.97 40 50 5.40 9.70 40 60 5.40 9.46 40 70 5.40 9.23 40 80 5.40 9.03 40 90 5.40 8.85 40 100 5.40 8.69 40 110 5.40 8.54 40 120 5.40 8.40 40 130 5.40 8.28 40 140 5.40 8.17 40 150 5.40 8.07 40 160 5.40 7.98 40 170 5.40 7.91 40 180 5.40 7.84 40 190 5.40 7.78 40 200 5.40 7.72 40 210 5.40 7.68 40 220 5.40 7.64 40 230 5.40 7.61 40 240 5.40 7.59 40 250 5.40 7.57

TABLE-US-00003 TABLE 3 Precipitated amounts of hydroxylapatite and pH values as a function of the temperature for the system 1000 g H.sub.2O + 5 g Ca.sub.3(PO.sub.4).sub.2 + 0.1 g HCl + 1 g CaCl.sub.2, addition of 0.38 g CaO p T Hydroxylapatite (s) (bar) (C.) (g) pH 40 20 5.40 9.98 40 30 5.40 9.65 40 40 5.40 9.35 40 50 5.40 9.08 40 60 5.40 8.84 40 70 5.40 8.62 40 80 5.40 8.42 40 90 5.40 8.24 40 100 5.40 8.07 40 110 5.40 7.92 40 120 5.40 7.79 40 130 5.40 7.67 40 140 5.40 7.56 40 150 5.40 7.46 40 160 5.40 7.37 40 170 5.40 7.29 40 180 5.40 7.22 40 190 5.40 7.16 40 200 5.40 7.11 40 210 5.40 7.06 40 220 5.40 7.03 40 230 5.40 7.00 40 240 5.40 6.97 40 250 5.40 6.95