Abstract:
A gasification reactor including a gasifier with a tubular gastight wall arranged within a pressure vessel. The tubular gastight wall is provided with one or more pressure relief passages sealed by a rupture element. The pressure relief passages can be provided with a cooled section, such as a double walled section confining a coolant channel.

Description:
PRIORITY CLAIM 
     The present application claims priority from PCT/EP2012/050951, filed 23 Jan., 2012, which claims priority from European patent application 11152040.9, filed 25 Jan., 2011, which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a gasification reactor comprising a gasifier with a tubular gastight wall arranged within a pressure vessel. 
     Gasification reactors can for instance be used for the production of synthetic gas by partial combustion of a carbonaceous feed, such as pulverized coal, oil, biomass, gas or any other type of carbonaceous feed. 
     Some gasification reactor types comprise a gasifier only having a discharge opening at its lower end for discharging syngas via a discharge—generally referred to as dip tube—into the slag collection bath. Due to the pressure build-up in the gasifier freshly produced synthetic gas containing slag and fly ash particles is forced to flow down through the dip tube and the slag collection bath around the lower edge of the dip tube to be recollected in the annular space between the dip tube and the pressure vessel wall. The water in the slag collection bath cleans and cools the synthetic gas. 
     During operation of the reactor, slag is continuously deposited on the inside of the gastight wall of the gasifier. Slag slides down from the inner surface of the gasifier wall and drops via the discharge opening into the slag collection bath. If the slag slides slowly the discharge opening in the gasifier is reduced by accumulation of slag lumps, which can eventually lead to blockage of the opening. This causes a build up of overpressure in the gasifier, which can cause substantial damage. 
     In other cases, an overpressure may develop in the annular space between the gasifier wall and the pressure vessel, for instance caused by a defect in the supply of water to the slag collection bath or by defective valves in the reactor&#39;s supply or discharge infrastructure. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to prevent damage of a gasification reactor caused by overpressure within the gasifier and/or overpressure in the space between the gasifier and the pressure vessel. 
     The object of the invention is achieved with a gasification reactor comprising a gasifier with a tubular gastight wall arranged within a pressure vessel, wherein the tubular gastight wall is provided with one or more passages sealed by a rupture element. 
     Accordingly, if the differential pressure over the gasifier wall exceeds a certain limit value, the one or more rupture elements will break and pressure within the gasifier is equalized with the pressure between the gasifier wall and the pressure vessel. 
     Suitable rupture elements include rupture discs, or bursting discs or diaphragms, blowout panels, blow-off panels and rupture panels or vent panels, which may be circular, square or rectangular or have any desired shape. Such discs or panels can for instance be constructed from carbon steel, stainless steel, graphite and nickel alloys of molybdenum, chromium, cobalt, iron, copper, manganese, titanium, zirconium, aluminum, carbon, and/or tungsten, such as Hastelloy® alloys of Haynes International, Inc., or any other suitable materials. 
     The one or more passages in the gasifier wall may for instance be provided with a sleeve with a cooled section extending outwardly from an opening in the gasifier wall. The cooled sleeve forms a heat sluice and creates an area with the same pressure as within the gasifier, but with substantially lower temperatures. This protects the rupture element from premature failure due to thermal loads. 
     To protect the gasifier wall against the high temperatures within the gasifier, the wall is generally cooled. To this end the gastight wall can for instance wholly or partly be built from interconnected parallel tubular coolant lines. In that case these tubular lines can be by-passed around the one or more openings. 
     Optionally, the sleeve can be provided with a refractory lining surrounding the sleeve&#39;s end around the opening. In that case, one or more sections of the tubular lines by-passing one of the openings can be embedded in the refractory lining around the sleeve section. 
     In order to be able to keep the space enclosed by the sleeve clean and open, the sleeve can for example be connected to a source of purging gas, e.g., by means of one or more nozzles directed towards the opening surrounded by the sleeve. The purging gas can be any inert gas, such as nitrogen, steam or clean product gas. 
     Optionally, the passages can branch into a first branch sealed by a first rupture element dimensioned to break at an overpressure limit in the gasifier, and a second branch sealed by a second rupture element dimensioned to break at an overpressure limit in a space between the gasifier and the pressure vessel wall. The rupture elements can be dimensioned to break at the desired pressure by dimensioning the thickness, concavity or convexity and by material selection. 
     To reduce the risk of damage by fly ash particles, the pressure relief passages can for instance be positioned at the top end of the gasifier, where the fly ash content is lowest. 
     An exemplary embodiment of the invention will now be described by reference to the accompanying drawing, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 : shows schematically a longitudinal cross section of an embodiment of a gasification reactor according to the present invention; 
         FIG. 2 : shows in detailed cross section a pressure relief passage in the gasification reactor of  FIG. 1 . 
     
    
    
       FIG. 1  shows a schematic cross section of an exemplary embodiment of a gasification reactor  1  according to the present invention. The gasification reactor  1  comprises a gasifier  2  in a tubular gastight wall  3  with a closed top end  4  and a conical lower section  5  narrowing down to an open lower end  6  which opens into a coaxially arranged cylindrical duct or dip tube  7 . The duct  7  opens into a slag collection bath  8  filled with water. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The gasifier  2  is arranged coaxially within a closed cylindrical pressure vessel  9 . Burners  10  extend from outside through the wall of the pressure vessel  9  and the tubular wall  3  into the gasifier  2  to partially combust pulverized coal or other types of carbonaceous feed. 
     The tubular wall  3 , its closed top end  4  and its conical lower end  5  are built from a plurality of parallel tubular lines  11 . The lines  11  are operatively connected to a coolant supply  13  and lead to a coolant discharge  12 . 
     During operation the gasifier content is heated to a temperature of 1200-1700° C. At these temperatures the carbonaceous feed is partially combusted to form synthetic gas loaded with slag and fly ash. Due to the pressure built-up in the gasifier  2  the gasifier content is forced to flow downwardly via the opening  6  and the duct  7  into the water of the slag collection bath  8 . The water of the slag collection bath  8  filters the syngas to remove fly ash and slag. The filtered syngas surfaces in the annular space  14  between the duct  7  and the pressure vessel  9 , where the pressure is substantially lower than in the gasifier  2  and the duct  7 . Here, the syngas is discharged via a discharge line  15 . 
     At its top end  4  the gastight wall  3  of the gasifier  2  comprises one or more pressure relief passages  20 , which are shown in more detail in  FIG. 2 . The pressure relief passage  20  comprises a hollow cylindrical double-walled sleeve  22  extending outwardly from the top end  4  of the tubular wall  3 . The sleeve  22  is connected to an opening  23  in the tubular wall assembly  3 . The sleeve  22  is double-walled to define an annular cylindrical coolant channel  24  between its double walls. The annular coolant channel  24  comprises a coolant inlet  25  and a coolant outlet  26 , operatively connected to a coolant supply and a coolant discharge, respectively (not shown). The coolant is usually water. 
     At the opening  23  the sleeve  22  is surrounded by a refractory box  27  comprising a metal casing  28  filled with a refractory material  29 . The refractory material  29  embeds by-pass sections  30  for by-passing the lines  11  of the tubular wall section  3  around the opening  23 . 
     At its end opposite to the opening  23  the double walled sleeve  22  is provided with a flange  31  connected to a lower flange  32  of a cylinder  33 . At its opposite end, the cylinder  33  comprises a top flange  34  connected in a gastight manner to a lid  35 . Optionally, the lid  35  can be provided with a passage for a connecting line for a pressure measurement device, enabling measurement of the pressure within the gasifier in the cooled environment of the double walled sleeve  22 . The cylinder  33  further comprises a first branch  36  and a second branch  37  branching off laterally under right angles in opposite directions. The outer end of the first branch  36  is sealed by a first rupture disc  38 , which is shaped and dimensioned to rupture if the differential pressure at both sides of the rupture disc  38  exceeds a given upper limit caused by an overpressure in the gasifier  2 . The outer end of the second branch  37  is sealed by a second rupture disc  39 , which is shaped and dimensioned to rupture if the differential pressure at both sides of the rupture disc  39  exceeds a given upper limit caused by an overpressure in the annular space between the gasifier  2  and the pressure vessel  9 . 
     Between the double walled section and the flange  31  the pressure relief passage  20  comprises a single walled cylindrical section  40  with a connection  41  for a feed line of a purging gas (not shown). The purging gas can be used to blow the inner side of the pressure relief passage  20  and the opening  23  clean and to keep it clean of fly ash deposits. 
     The cooled section of the pressure relief passage  20  thermally shields the rupture discs  38 ,  39  from the gasifier content, which can be as hot as 1200° C. or higher. The pressure relief passage  20  forms a heat sluice which can for instance also be used for measuring the pressure in the gasifier in a cooled environment.