Abstract:
The loaded wash liquid contains H 2 S, CO, H 2 , CO 2 , nickel carbonyl and/or iron carbonyl. Carbon monoxide is initially and partially removed from the loaded wash liquid and the wash liquid which is low in CO is conducted through a reaction and settling zone. Sludge containing nickel and/or iron sulfide is extracted from the reaction and settling zone and the wash liquid is conducted to a heat regeneration device The regenerated wash liquid can be re-utilized for desulfurization purposes.

Description:
DESCRIPTION  
         [0001]    This invention relates to a process of regenerating a loaded washing liquid which comes from a plant for desulfurizing a gas mixture containing hydrogen and carbon oxides and as load contains H 2 S, CO, H 2 , CO 2 , and nickel carbonyl and/or iron carbonyl, where the washing liquid is reused for desulfurizing after a hot regeneration.  
           [0002]    Desulfurizing processes and the associated regeneration of loaded washing liquids are known and described for instance in the German patent 39 22 785 and in the corresponding U.S. Pat. No. 5,085,675. The regeneration of the loaded washing liquids is effected in a known manner by means of one or several of the measures expanding, stripping and heating, where it is also possible to perform two or three of these measures at the same time in one container.  
           [0003]    In particular when using physically acting washing liquids, metal carbonyls may lead to problems during the regeneration, as they are converted to sulfides during the heating of the washing agent and form undesired deposits. These carbonyls chiefly include nickel carbonyls, e.g. Ni(CO) 4 , and iron carbonyls, in particular Fe(CO) 5 . It is therefore the object underlying the invention to convert the metal carbonyls to sulfides at an appropriate point and remove them from the washing liquid to such an extent that difficulties in the desulfurizing plant and in subsequent plants are avoided. In accordance with the invention this is achieved in the above-mentioned process in that carbon monoxide is at least partly removed from the loaded washing liquid, the washing liquid poor in CO is passed through a reaction and settling zone, a sludge containing nickel sulfide and/or iron sulfide is withdrawn from the reaction and settling zone, and the washing liquid is supplied to the hot regeneration.  
           [0004]    In the nickel carbonyls and iron carbonyls the CO is coordinatively bound to the metal atom, so that the carbonyls are converted to sulfides (NiS or FeS) in the loaded washing liquid, as soon as the CO is at least partly removed from the washing liquid. This removal of CO can be effected in various ways, and in particular by means of expanding and/or stripping the washing liquid. The temperature of the loaded washing liquid should favorably be increased, for example, by means of an indirect or direct heat exchange with hot-regenerated washing liquid prior to the removal of CO.  
           [0005]    Usually, the desulfurization is effected at a pressure in the range from 10 to 100 bar, so that before the reaction and settling zone the loaded washing liquid can easily be expanded by a pressure difference of at least 3 bar, where a CO-containing expansion gas is released. After this release of CO, the nickel carbonyls and iron carbonyls in the washing solution are gradually converted to insoluble sulfides. It may be expedient to wash the released expansion gas with regenerated washing liquid, so as to keep carbonyls in solution.  
           [0006]    Preferably, the pressure in the reaction and settling zone lies in the range from 1 to 20 bar and mostly around at least 3 bar, the temperature usually lies in the range from 0 to 150° C. and preferably around at least 40° C. Advantageously, it should be ensured that the H 2 S contained in the loaded washing liquid and also the CO 2  are not, or possibly only to a minor extent, released in the reaction and settling zone and only the nickel sulfides and/or iron sulfides are precipitated there. It is therefore expedient to keep the pressure in the reaction and settling zone higher than in the hot regeneration.  
           [0007]    To achieve an optimum separation of the metal sulfides from the washing liquid in the reaction and settling zone it is recommended to pass the washing liquid through the reaction and settling zone with a sufficient dwell time, and move the washing liquid as slowly as possible, so that the sulfides can gradually settle. For nickel carbonyls, dwell times in the range from 5 to 80 minutes and mostly 15 to 60 minutes are usually sufficient, whereas iron carbonyls require dwell times of about 1 to 10 hours, preferably at least 3 hours.  
           [0008]    The process in accordance with the invention is suited for the treatment of different washing liquids, e.g. methanol, N-methylpyrrolidone (NMP) or dimethyl ether of polyethylene glycol (DMPEG). Usually, these are physically acting washing liquids. The gas mixture to be desulfurized comes from the gasification of solid or liquid carbonaceous materials, e.g. heavy oil, coal, petroleum coke, hydrocarbons containing asphalt, distillation residues or mixtures of these materials. The gasification is effected in a known manner by means of a partial oxidation with air, with oxygen-enriched air or with technically pure oxygen, and mostly by adding steam.  
       
    
    
       [0009]    Embodiments of the process will be explained with reference to the drawing, wherein:  
         [0010]    [0010]FIG. 1 shows the flow diagram of a plant for treating a gasification raw gas and for regenerating a loaded washing liquid,  
         [0011]    [0011]FIG. 2 shows a horizontal section along line I-I through the reaction and settling vessel of FIG. 1 in an enlarged representation,  
         [0012]    [0012]FIG. 3 shows the view of the inlet pipe of the reaction and settling vessel of FIGS. 1 and 2, viewed opposite to the direction of the arrow A in FIG. 2, and  
         [0013]    [0013]FIG. 4 shows a variant of the flow diagram of FIG. 1. 
     
    
       [0014]    The process illustrated in FIG. 1 is based on the fact that a heavy oil is gasified by means of a partial oxidation, but the process in accordance with the invention can also be used in plants for gasifying other solid or liquid materials.  
         [0015]    Heavy oil is supplied to the empty gasification reactor  1  through line  2 , and this heavy oil is gasified with oxygen from line  3  and steam from line  4  at temperatures in the range from 800 to 1400° C. A raw gas containing hydrogen, carbon oxides and soot is obtained, which is passed through the passage  6  into a washer-cooler  7 , in which the raw gas is sprayed with water from line  8 . Sooty water is withdrawn via line  9 . The roughly cleaned raw gas is supplied via line  10  to a spray cooler  11 , in which the gas is sprayed with partly circulating water and subjected to further cooling. The water flowing out of the cooler  11  via line  12  is partly removed via line  13 , the remaining water is supplied to an indirect cooler  15  through line  14  and is recirculated to the cooler  11  by means of the circulating pump  16 . Fresh water comes from line  17 .  
         [0016]    Through line  19 , the gas mixture treated in the spray cooler  11  is supplied to a desulfurization column  20 , where in a counterflow with washing liquid from line  21  it is above all largely liberated from H 2 S. Purified gas is withdrawn via line  22 .  
         [0017]    The pressure and the temperature in the desulfurization column  20  are appropriately chosen in a known manner adapted to the used washing liquid, where the use of NMP provides for higher temperatures than the use of methanol as washing liquid. Usually, the temperatures in the desulfurization column  20  lie in the range from +60° C. to −60° C., and there is employed a pressure in the range from 10 to 100 bar.  
         [0018]    The loaded washing liquid, which is withdrawn from the column  20  via line  25 , contains H 2 S, CO 2 , CO, H 2  and, depending on the metal content in the material to be gasified, also nickel carbonyls and/or iron carbonyls. In the indirect heat exchanger  26  the loaded washing liquid is heated and then expanded into the expansion vessel  27 . Expediently, the pressure in the vessel  27  is lower than in the desulfurization column  20  by at least 3 bar and preferably by at least 5 bar.  
         [0019]    During the expansion of the loaded washing liquid into the expansion vessel  27  an expansion gas is released, which also contains carbon monoxide. This expansion gas is withdrawn via line  28  and is first passed through the cooler  50  and then through the washing column  51 , in order to remove carbonyls released during the expansion. Regenerated washing liquid comes from line  21   a  and upon usage is delivered to the vessel  27  via line  52 .  
         [0020]    To further increase the expulsion of CO in the vessel  27 , it may be advantageous to additionally introduce a stripping gas, e.g. nitrogen or methanol vapor, through line  29  into the lower portion of the expansion vessel  27 . Alternatively, such stripping may also be effected in a separate column. The partly expanded washing liquid is then supplied through line  30  to a reaction and settling vessel  31 , details of which are represented in FIGS. 2 and 3. In the vessel  31  a sulfide sludge is precipitated, which above all consists of nickel sulfide and/or iron sulfide and is withdrawn via line  32 . The washing liquid largely liberated from carbonyls flows from the vessel  31  through line  34  into the hot regeneration  35 , where H 2 S is removed during the regeneration. In contrast to the simplified representation of FIG. 1, the hot regeneration can also consist of several treatment stages and for instance additionally employ a supply of stripping gas.  
         [0021]    Regenerated washing liquid is withdrawn via line  36 , is cooled in the indirect heat exchanger  26  and is recirculated through line  21  to the desulfurization column  20  and the column  51 . The regeneration exhaust gas, which is produced in line  38  and chiefly consists of H 2 S, may be supplied to a Claus plant known per se, which is not represented here.  
         [0022]    Details of the reaction and settling vessel  31  are explained with reference to FIGS. 2 and 3. In this vessel  31  it is ensured that the washing liquid flows from the inlet pipe  40  to the outlet pipe  41 , slowly and with a sufficient dwell time. At the same time, a maximum height of the liquid of 2 to 40 m is ensured. To achieve that the sulfides formed can settle in the vessel  31  as unimpededly as possible, the liquid flows horizontally from the inlet pipe  40  through numerous apertures  42 , see FIG. 3, first in the direction of the arrow A along a zigzag path formed by partitions  43 , see FIG. 3, to the outlet pipe  41 . The outlet pipe  41  may likewise be provided with apertures, as is represented in FIG. 3 for the inlet pipe. The liquid arriving in the outlet pipe  41  flows off in the collecting line  34  and is delivered to the hot regeneration  35 . During the approximately horizontal flow of the washing liquid from the inlet pipe  40  to the outlet pipe  41  the sulfides formed may settle to the bottom, accumulate in the sump  31   a  of the vessel  31  (see FIG. 1) and be withdrawn through line  32 . To prevent the sulfides from also accumulating in the inlet pipe  40 , there is likewise provided a discharge line  45  including a valve  46  (see FIG. 3).  
         [0023]    The sulfide sludge settling at the bottom of the vessel  31  is periodically withdrawn through line  32  by opening a valve not represented and is delivered into the heated treatment vessel  55 . Vapors of the washing liquid are delivered through line  56  into the hot regeneration  35 . If necessary, washing water may be introduced into the vessel  55  through line  57 . The sulfide sludge withdrawn via line  58 , which now contains less noxious substances, is introduced into a not represented collecting tank.  
         [0024]    In the procedure represented in FIG. 4 it is ensured that washing liquid chiefly containing iron carbonyls can be withdrawn at least partly separate from washing liquid chiefly containing nickel carbonyls. For this purpose, the desulfurization column  20 , which has already been described in conjunction with FIG. 1, is provided with a gas-permeable bottom  60 . The gas mixture entering through line  19  is first of all brought in contact with a partial stream of the regenerated washing liquid, which comes from line  21   a . Iron carbonyls are preferably absorbed by the liquid and delivered through the indirect heat exchanger  26 , the expansion vessel  27  and line  30  to the reaction and settling vessel  31 . In the vessel  31  a relatively long dwell time of 1 to 10 hours and mostly of several hours is ensured, before the sludge containing iron sulfide is withdrawn through line  32 . Small amounts of NiS are likewise contained in the sludge in line  32 .  
         [0025]    The partial amount of used washing liquid, which is withdrawn via line  25   a,  is delivered through the heat exchanger  26   a  and the expansion vessel  27   a  to the second reaction and settling vessel  31   a . After a relatively short dwell time of 5 to 80 minutes, a sludge chiefly containing nickel sulfide can then be withdrawn through line  32   a.    
       EXAMPLE  
       [0026]    In a procedure in accordance with FIG. 1 raw gas from the gasification of heavy oil is desulfurized. Raw gas is supplied to the desulfurization column  20  in an amount of 6690 kmol/h with the following composition:  
                                                       CO 2     5.4 mol-%           CO   47.7 mol-%            H 2     45.3 mol-%            CH 4     0.2 mol-%           N 2     0.3 mol-%           H 2 S   0.9 mol-%           COS   0.2 mol-%                      
 
         [0027]    This raw gas still contains 1.6 ppmv iron carbonyl and 1.2 ppmv nickel carbonyl. The pressure in the column  20  is 55 bar, and the temperature in the lower portion of the column  20  is about −26° C. Cold methanol is supplied to the column in an amount of 3100 kmol/h as washing liquid.  
         [0028]    The loaded washing liquid flowing off via line  25  contains 5.6 mol-% CO 2 , 1.1 mol-% CO and 0.4 mol-% H 2  as well as all sulfur components and carbonyls of the raw gas in dissolved form. With a temperature of 90° C., the washing liquid enters the expansion vessel  27 , which operates without supply of stripping gas. The pressure in the vessel  27  is 8 bar. The expansion gas, which leaves the column  51  in an amount of 170 kmol/h via line  28   a,  contains  
                                                       CO 2     64.8 mol-%            CO   21.2 mol-%            H 2     7.0 mol-%           H 2 S   6.5 mol-%           COS   0.5 mol-%                      
 
         [0029]    This gas had been washed with 125 kmol/h cold methanol from line  21   a.    
         [0030]    The pressure in the vessel  31  is about 8 bar, and the temperature is 85° C. After a dwell time of 5 hours, the loaded washing liquid is supplied to the hot regenerator  35  via line  34 . During the dwell time in the vessel  31 , 100% of the nickel carbonyls and 98% of the iron carbonyls are converted to sulfides, which settle down and are withdrawn as sludge.