Abstract:
A process is described for the flash pyrolysis of a high rank caking coal in a pyrolysis chamber in which the coal passes through a tacky state during flash pyrolysis. According to the novel feature, before entering the pyrolysis chamber, the particles of high rank caking coal are blended with a diluent comprising a finely ground non-caking coal, whereby agglomeration and caking of the high rank coal is prevented during flash pyrolysis.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to the flash hydropyrolysis of high ranking caking (agglomerating) coals, such as bituminous coal, to produce gaseous, liquid and solid decomposition products. More particularly, it relates to a process in which high rank caking coals can be flash hydropyrolyzed in a tubular reactor or a fluidized bed reactor. 
     Pyrolysis or carbonization of coal and other carbonaceous solids is a well-established technique. It comprises heating carbonaceous material to temperatures at which thermal decomposition occurs with the formation of condensible organic liquids, non-condensible gases and solid residue. The condensible organic liquids obtained are normally referred to as tars and light oils, while the solid residue is normally referred to as char. The tar as produced by the process can be further refined with hydrogen to produce a range of liquid fuel products. 
     The total yields of tar and liquid hydrocarbons from pyrolysis of coal and other carbonaceous material are markedly influenced by pyrolysis conditions such as heating rate, temperature and residence time of the liberated volatiles and coal particles in the pyrolysis zone. When coal is subjected to rapid or flash pyrolysis followed by rapid quenching of the volatile products, the yields of liquids from the process are maximized and secondary decomposition of the tar product is minimized. This concept of flash pyrolysis has been widely accepted as a carbonization technique for the production of oil from coal. 
     Flash hydropyrolysis must be carried out at very high heating rates of the coal particles and also with very low residence time of the volatiles in the pyrolysis zone. These conditions are readily met by processing finely divided coal particles in either a fluidized bed or entrained flow reactor. 
     Problems are experienced when caking coals, e.g. bituminous coals, are used in flash pyrolyzers because it is necessary to take the coal particles through a temperature range at which they become plastic, and in which stage the coal particles tend to agglomerate or cake, before good yields of volatiles are obtained. With caking coals, severe build up of caked or agglomerated char can occur in the pyrolyzer or the product outlet lines, or in both. These caked or agglomerated char deposits can adversely affect the operating characteristics of the pyrolyzer and can ultimately render the process inoperable. 
     Various techniques have been proposed for overcoming or reducing the problems experienced with agglomerating or caking coals. For instance, the caking carbonaceous material may be mixed with non-agglomerating materials such as hot char. One such process is described in Sass et al., U.S. Pat. No. 3,736,233. However, when the caking coal particles are diluted by mixing them with non-agglomerating solid material, such as char, the quantity of recycled char required is excessively large when this material is derived from an external source, and internal recycling of char or other inert material introduces an additional hot surface which enhances the cracking reactions with a resultant loss in char yield. Moreover, the use of a large amount of inert materialreduces the reactor efficiency by occupying a significant portion of the effective reactor volume. 
     It is an object of the present invention to provide a new and simplified technique for overcoming the agglomeration or caking problems associated with the flash pyrolysis of caking coals. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a continuous process for the pyrolysis of high rank agglomerative or caking coals, such as bituminous coals, in which the coal passes through a tacky state during pyrolysis without forming deposits thereof on the reactor walls. In the present invention, the agglomeration problems associated with the tacky state are avoided by mixing the high rank caking coal with a finely ground low rank non-caking coal, such as partially oxidized coal, sub-bituminous coal and lignites, to prevent agglomeration and caking of the high rank coals during the flash pyrolysis. 
     The non-caking coal should be ground to a very fine particle size of typically less than 40 microns and preferably less than 10 microns. The effective concentration of non-caking coal diluent depends on the swelling index, the wetability of the diluent by tarry substances that exude from the caking coal particles, and the relative particle diameter of the caking coal to that of the diluent. 
     For use in the process of this invention, the particle size of the high rank caking coal can vary quite widely, e.g. from about -35 mesh to +150 mesh (Canada standard sieve). 
     The blend of caking coal and non-caking coal typically contains about 10 to 50%, preferably 20 to 50%, by weight of the non-caking coal and it may also include a small amount, e.g. in the range of about 1 to 5% by weight, of a finely divided inert material, such as silica powder. This aids in the inhibition of caking. 
     In the method of the present invention, the above mixture is fed into a tubular or fluidized bed flash pyrolyzer at a temperature in the range of about 500° C. to 950° C. and a pressure of at least 4.0 MPa. Preferably the temperature is maintained at a level above 600° C. with a retention time of coal in the reaction zone of under 10 seconds. 
     Many different materials were tried as diluent for caking coals for instance, lime and Prince Mine char were tested as diluents at particle sizes of less than 10 microns. Even though the lime and char were very finely divided, their surface properties were such that caking could not be reduced substantially during flash hydropyrolysis. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following examples are illustrative of the concept of this invention, demonstrating the method of preventing agglomeration of coal during flash hyropyrolysis. 
     EXAMPLE 1 
     A series of experiments were carried out to determine the effectiveness of various diluents as caking inhibitors. As bituminous coals for these experiments there were used Prince Mine bituminous coal (PMC) and Lingan bituminous coal (LC). Both coals were ground to less than 60 mesh (less than 250 microns) before being mixed with diluents. The diluents used were Forrestburg sub-bituminous coal (FC), Prince Mine coal char lime and Cab-O-Sil (trade mark for extremely fine silica sold by Cabott Corp.). The Forrestburg sub-bituminous coal was ground to less than 40 microns particle size and to less than 10 microns particle size for different tests. The lime and Prince Mine char were ground to less than 10 microns particle size, while the Cab-O-Sil had a particle size of less than 1 micron. 
     Different amounts of diluent between 3% and 65% by weight were mixed with the bituminous coal samples and the mixtures then served as feed stocks to a tubular flash pyrolyzer. These were subjected to a temperature of 700° C., for 2.5 minutes. 
     The results obtained from hot pour tests are shown in Table 1 below. 
     
                                           TABLE I__________________________________________________________________________Hot Pour Tests                      Char Remainder                              Char Remainder        WT % of              Char    In Crucible                              In Crucible                                      Segregation        Diluent              Fluidity                      Fluidity When                              Fluidity When                                      NotedCoal  Diluent        In Charge              Hot     Cold    Tapped  In Charge__________________________________________________________________________PMC   None   0     Button  Button  --      None-40 PMC None   0     Button  Button  --      NonePMC   -40 m F.C.        50    90% Pours                      10% Pours                              --      NonePMC   -40 m F.C.        30    50% Pours                      Little Pours                              45% Pours                                      NonePMC   -40 m F.C.        15     5% Pours                      Little Pours                               5% Pours                                      NonePMC   -40 m F.C.        5     Button  Button  --      NonePMC   -10 m F.C.        30    20% Pours                      Little Pours                              10% Pours                                      NonePMC   -10 m F.C.        15    No Fluidity                      Little Pours                              Little Pours                                      NonePMC   -10 m F.C.        5     Button  Button  --      NonePMC   Cab-O-Sil        10    100% Pours                      --      --      SomePMC   Cab-O-Sil        5     90% Pours                       5% Pours                               5% Pours                                      NonePMC   Cab-O-Sil        3     50% Pours                      10% Pours                              10% Pours                                      SomePMC   Lime   50    95% Pours                       2% Pours                               3% Pours                                      SignificantPMC   Lime   40    80% Pours                      10% Pours                              10% Pours                                      SignificantPMC   Lime   20    Button  Button  --      SignificantPMC   -10 m Char        20    Partial Button                      Button  --      NonePMC   -10 m Char        15    Partial Button                      Button  --      NonePMC   -10 m Char        5     Button  Button  --      NoneLC    -40 m F.C.        65    95% Pours                      Little Pours                               5% Pours                                      NoneLC    -40 m F.C.        55    95% Pours                      Little Pours                               5% Pours                                      NoneLC    -40 m F.C.        30    90% Pours                      Little Pours                              Little Pours                                      NoneLC    -10 m F.C.        50    95% Pours                       5% Pours                              --      NoneLC    -10 m F.C.        30    85% Pours                       5% Pours                              --      NoneLC    -10 m F.C.        15    10% Pours                      Nothing Pours                              Nothing Pours                                      NoneLC    -10 m F.C.        5     Button  Button  Button  None__________________________________________________________________________ PMC  Prince Mine Coal LC  Lingan coal 
    
     It can be seen from Table 1 that the sub-bituminous coal particles represent the most effective caking inhibitors. 
     EXAMPLE 2 
     A further series of tests were conducted in which the feed stock was a blend of Prince Mine bituminous coal, Forrestburg sub-bituminous coal and Cab-O-Sil. The proportions of these materials used, the reactor conditions and the results obtained are set out in Table II below. 
     
                       TABLE II______________________________________Test Data for Class `A` Runs(Successful Runs)Test #           66      64      60    63______________________________________Prince Mine Coal       %        57      57    57    57Forestburg Coal       %        40      40    40    40CAB-O-SIL            3       3     3     3React. Heaters `on`       #        4       4     3     2Date        moth.day 4.11    4.03  3.21  4.01Duration    min      76      46    68    65Reactor pressure       psi      1800    1880  1800  1800Reactor pressure       MPa      12.4    13.0  12.4  12.4Coal (dry) fed       9        597     446   610   589Coal feed rate       g/h      472     582   538   544Hydrogen feed rate       g/h      1106    913   1257  973Power into pre-       kVA      3.3     3.2   3.6   2.7heaterHydrogen preheat       C.       725     740   705   680Heated reactors       C.       800     800   800   800set toGas temp. inside       C.       700     715   # N/A # N/Areact.Reactor wall #1/#2       C.       700     # N/A # N/A # N/AReactor wall #3/#4       C.       #N/A    718   640   475Gas discharge temp.       C.       670     665   530   375Gas velocity       cm/s     13      10    15    12Particle velocity       cm/s     24      28    29    29Gas residence time       s        21      26    14    12Particle resid. time       s        7       7     5     3First liquid trap:Organic Liquids       % coal   5.5     3.9   6.8   3.2Process water       % coal   11.7    11.9  10.3  10.2Solids      % coal   2.0     0.2   0.6   0.0Total collected       % coal   17.4    17.8  17.7  13.5Second liquid trap:Organic Liquids       % coal   1.6     4.5   8.3   3.8Process water       % coal   0.9     0.4   0.2   0.0Solids      % coal   0.0     0.1   0.2   0.1Total collected       % coal   2.6     5.0   8.6   3.9Char trap   % coal   41.8    40.0  43.2  54.7Organic Liquids       % coal   7.1     8.4   15.1  7.0Gaseous HC&#39;s       % coal   37.2    42.1  31.3  26.4CO &amp; CO2    % coal   5.5     5.1   5.5   5.5Char (total)       % coal   42.0    42.1  44.0  54.9Process water       % coal   12.7    12.3  10.5  10.2All porducts *       % coal   104.5   110.0 106.4 104.1______________________________________ 
    
     A mass balance was also conducted on the runs from Table II above and the results obtained are shown in Table III below. 
     
                       TABLE III______________________________________Mass Balances for Class &#34;A&#34; RunsTest #             66     64     60    63______________________________________Prince Mine Coal          %       57     57   57    57Forestburg Coal          %       40     40   40    40CAB-O-SIL      %       3      3    3     3React. Heaters `on`          #       4      4    3     2Heated reactors set to          C.      800    800  800   800Gas temp. inside react.          C.      700    715  # N/A # N/AReactor pressure          psi     1800   1880 1800  1800Hydrogen preheat          C.      725    740  705   680Gas discharge temp.          C.      670    665  530   375Coal feed rate g/h     472    582  538   544Hydrogen feed rate          g/h     1106   913  1257  973Coal conv., MAF basis          % coal  65.1   64.6 62.7  49.2Hydrogen feed rate          % coal  234.6  157.0                              233.5 179.0Unreacted H in effluents          % coal  227.4  148.3                              227.4 173.7H added to products          % coal  7.3    8.7  6.1   5.3Coal (dry)     % coal  100.0  100.0                              100.0 100.0FEED           % coal  107.3  108.7                              106.1 105.3Organic Liquids          % coal  7.1    8.4  15.1  7.0Process water  % coal  12.7   12.3 10.5  10.2LIQUID PRODUCTS          % coal  19.8   20.7 25.6  17.2Gaseous HC&#39;s   % coal  37.2   42.1 31.3  26.4CO &amp; CO2       % coal  5.5    5.1  5.5   5.5GASEOUS PRODUCTS          % coal  42.7   47.2 36.8  31.9CHAR           % coal  42.0   42.1 44.0  54.9ALL PRODUCTS   % coal  104.5  110.0                              106.4 104.1UNACCOUNTED    % coal  2.8    -1.3 -0.3  1.3______________________________________ 
    
     The above mass balances close within 3 weight %, indicating satisfactory operation. 
     While we have described particular embodiments of our invention for purposes of illustration, it is understood that other modifications and variations will occur to those skilled in the art, and the invention accordingly is not to be taken as limited except by the scope of the appended claims.