CA2008920A1

CA2008920A1 - Preparation of synthesis gas by partial oxidation

Info

Publication number: CA2008920A1
Application number: CA002008920A
Authority: CA
Inventors: Gero Lueth; Rolf Becker; Robert K. Horn; Uwe Kempe; Wolfgang Vodrazka
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1989-01-31
Filing date: 1990-01-30
Publication date: 1990-07-31
Also published as: US4999029A; EP0380988A2; DE59004958D1; JPH02239101A; EP0380988A3; ATE102894T1; ES2050284T3; EP0380988B1; DE3902773A1

Abstract

- 13 - O.Z. 0050/40532 Abstract of the Disclosure: Synthesis gases are prepared by partial autothermal oxidation of liquid fuels and/or solid fuels in the presence of oxygen or oxygen-containing gases with the addition of a temperature moderator, such as steam and/or CO2, in an empty reactor space without baffles, at from 1000 to 1500°C under from 1 to 100 bar, the reactants fuel and oxygen-containing gas being fed separately to the reactor, by a process in which the steam or CO2 is fed in simultaneously with the feed of the fuel, and the steam is let down through one or more nozzles into the fuel stream directly before the orifice for the fuel, let-down being effected at from 30 to 250%, preferably from 80 to 140%, of the critical pressure ratio. An apparatus for carrying out the process is also described.

Description

O.z. 0050/40532 Preparation of synthesis gas by partial oxidation It is known that synthesis gas, which contains CO, H2, H2O and CH4 and may contain N2, can be prepared by partia~ oxidation of liquid hydrocarbons, very finely milled solid fuels or mixtures of the two in the presence of oxygen or oxygen-containing gases, such as air or oxygen-enriched air.
Occasionally, in addition to tha production of C~
and H20, it is also de~irable to form methane (U.S. Patent 3,951,617), in order to obtain gases having a higher calorific value. In proce~e~ controlled in this way, a particularly large amount of carbon black i8 obtained owing to the low temperatures required.
The known processes operate as a rule under from 1 to 100, preferably from 30 to 80, bar, the fuel being reacted with oxygen or an oxygen-containing gas, in an empty, lined reactor without baffles, to give a ga~ mix-ture consi~ting of a plurality of components. In general, the mixture contains CO2, CO, CH~, COS, H~O, H2S, H2 and N2. In addition, depending on the number of carbon atoms in the fuels used, increasing amounts of carbon black or coke are formed, which have to be separated off from the cleavage gas by expensive processes (eg. U.S.
Patents 3,980,590, 3,980,591 and 3,980,592) and may have to be recycled to the proce~. Where the fuels have a high ash content, some of the resulting carbon black or coke mu~t always be removed. Recycling with the fuel used may lead to an undesirable accumulation of slag in the reaction space.
The process, in which the liquid fuel is sprAyed via a single-material nozzle under high pre~sure into the oxygen/steam stream, has the disadvantage that the nozzle size, nozzle pressure and oil viscosity (oil temperature) have to be adapted to one another in order to ensure an optimum distribution of the fuel in the oxygen/steam ~tream. For a given nozzle, only small changes in load are po3sible. As a rule, operation at part load Z~920 - 2 - O.Z. 0050/40532 nece~-qitates a nozzle change, which entails a shutdown.
Furthermore, the fine nozzle channels are very sensitive to relatively coarse solid particles in the oil.
Blockages lead to non-uniform combustion, which may occasionally lead to rupture of the reactor wall and gaq blow-outs.
The known industrial processes differ in general in the method of carbon black removal and working up and/or in the feed of the reaction products to the reactor.
We have found that the disadvantages of the known processes u~ing fuel~ having a high ash content are avoided if, in the preparation of ~ynthesis ga~es by par-tial autothermal oxidation of liquid fuels and/or solid fuels in the presence of oxygen or oxygen-containing ga~es with the addition of a temperature moderator, such as steam and/or CO2, in a reaction space without baffle~
at from 1000 to 1500C under from 1 to lOO bar, the reac-tants fuel and oxygen-containing gas being fed separately to the reactor, the steam and/or CO2 i~ or are fed in simultaneously with the fuel, and the ~team is let down through one or more nozzles into the fuel stream, direct-ly before the orifice for the fuel, let-down being effected at from 30 to 250%, preferably from 80 to 140%, of the critical pressure ratio.
Let-down is preferably effected at from 80 to 140% of the critical pressure ratio. The critical pres-surQ ratio i8 obtained when th~ nozzle pre~sure i~ equal to E~p - (X 1 ) time~ the reactor pressure, where X is the adiabatic exponent.
For example, if X = 1.3, the initial nozzle pres-sure is 1.83 times the reastor pre~sure.
The present invention furthermore relate~ to an 2 [)1~89~0 - 3 - o.Z. 0050/40532 apparatus for carrying out the process, consisting of an empty reactor which i9 free of baffles, having a three-stream burner with in each case one or more separate feeds for fuel (2) and oxygen (3) to the water-cooled burner mouth (5) and parallel feed of steam and/or carbon dioxide, the pipe for the ~team (1) being laid concentrically inside the pipe for the fuel, and the steam being let down into the oil through a central nozzle which ends flush with the orifice of the fuel pipe or ~p to 5 times the diameter of the fuel pipe, in the direction of flow, before the said orifice, and a cooling water feed (4).
According to the invention, when a ga~ having a high oxygen content and liquid hydrocarbons are u~ed, a temperature moderator is added in an amount which limits the temperature to about 1300-1500C, ie. the temperature range in which tha highest conver~ion rat0s are achieved.
If methane formation is to be promoted, the temperatures must be reduced to about 1000-1200C. In general, steam i~ used as the moderator, in an amount of from 0.05 to O.8, preferably from 0.2 to 0.4, times (w/w) the amount of fuel. However, it is also possible to use C~2 if a CO-rich gas is desired, in which case the amounts may occasionally also be increased and the CO2 recycled after scrubbing of the cleavage gas.
According to the invention, ~team is predominant-ly used as the moderator. The novel process constitutes a novel method for introducing liquid fuels and ~uspen-~ions of solid fuels in liquid fuels or in water into the reaction space and controlling the reaction in an optimum manner.
In the novel process, in which fuel and oxygen and steam or CO2 are fed into the reaction space through a three-stream burner (Figure 1), the stated disadvan-tages are not encountered ~ince the load can be variedwithin a wide range, starting from the maximum load.
Where two-stream burner~ are u~ed, disper~ion of the 9~o - 4 - O.Z. 0050/40532 liquid fuel with the moderating steam may al~o be ef-fected out~ide the reactor, before the burner, in a mixer. Downstream of the mixer, the oil/steam mixture can be~fed to the burner through the pipe, and emerges S through the annular gap and mixes with the oxygen in the reactor, with further disper~ion of the oilO The load can be reduced to about 60%. In spite of this wide load range of the burner, however, the quality of gasification depends on the load in thi~ proces~ too, a~ shown in Examples 2 and 3.
The equilibrium concentration (G in Figure 2) of CO2 in the presence of carbon at 1350C and 40 bar total pressure of 45~ of CO is about 0.5% of CO2 in the cleav-age gas. The effective CO2 content in the cleavage gas at a certain carbon black concentration in the cleavage gas, expressed in kg of carbon black per 100 g of fuel, is a mea~ure of the approach to equilibrium and hence of the conver~ion in the gasification reaction.
On the other hand, a small amount of carbon black for a given CO2 content in the cleavage gas means that the gasification conditions are advantageous.
In the graph (Figure 2), in which the amount of carbon black obtained is plotted in kg of carbon black/
100 kg of oil along the ordinate and the COz content i8 plotted along the abscissa, the quality of gasification is clearly shown. Values denoting the same quality of ga~ification lie along a hyperbola who~e vertical branch approximates to the CO2 equilibrium content in the cleav-age gas while the horizontal branch approximates to the abscis~s axis. If carbon is no longer present, CO2 can no longer be converted into CO. The clo~er the vertex of the hyperbola approache~ the point of intersection of the CO2 equilibrium concentration and the absci~a axis, the better the quality of gasification and the smaller the gasification losses of carbon black and CO2. Higher CO2 values in the cleavage gas can be obtained by a greater amount of moderating steam coupled with higher ~pecific 2~ 920 _ 5 - o.Z~ 005~/40532 oxygen. The lowest CO2 content~ are achieved with very little moderating steam, for example s O.2 t of steam/t of fuel. Thus, the amount of carbon black obtained in-creases for a given quality of gasification.
The hyperbolic sections A to D in Figure 2 correspond to increasing quality of gasification.
The point~ are the measurements of Examples 1 to 6:
(1) 10 t/h of steam ) (2) 10 t/h of steam ) ~ two-stream burner (3) 12 t/h of steam ) (4) 10 t/h of steam ) t5) 10 t/h of steam ) ~ three-stream burner accordingto (6) 12 t/h of steam ) the novel process We have found that, with conventional two-~tream burners, the quality of gasification defined above becomes markedly poorer both at low load and at normal load with the use of oils having a relatively high vis-cosity and in particular with the use of residue oils containing very small amount~ of readily volatile com-ponents. Only when relatively large amounts of oxygen and steam are used i9 it possible to keep the amount of carbon black produced within acceptable limits. This i8 particularly important when it is desired to avoid the expensive recycling of carbon black to the feed fuel and to transport the carbon black washwater to another treatment.
~he novel po~itioning of the stea~ feed into the liquid fuel close to the outlet orifice, and the mixing of the steam with the oil via a nozzle at a critical pressure drop of 30 to 250~, preferably from 80 to 140%, lead to a surprising improvement in the quality of ga~-ification. With very little steam and very little excess oxygen, a synthesis ga~ is obtained which has a very low COz content and little carbon black as a byproduct, ie.
the quality of ga6ification increases sharply.

2~0892~) - 6 - O.Z. 0050/40532 We have furthermore found that it i~ also pos-~ible to let down only some of the nece~ary moderating steam into the oil stream and then to add the remaining part of the moderating steam to the oxygen or to the fuel. It is thu~ po~sible for the amount of steam let down into the oil via the nozzles to be kept o small that it i8 sufficient at part load. At normal load, the additional moderating steam required is added via the oxygen.
The novel process thus combines the advantage~ of the favorable gasification conditions with the advantage of great flexibility in the reactor load. How~ver, higher yields are obtained even in the gasification of relatively highly viscou~ residue oils which have a low content of volatile component~.
A positive side effect of the novel process is that the solid particles always obtained in the partial oxidation process are substantially smaller. There i8 therefore likely to be les~ wear in the downstream waste heat system.

In a synthesis gas generator operated under 40 bar, 10 t/h of a high boiling vacuum residue i~ intro-duced via a two-stream burner, tha oil is predi~persed with 2.8 t of steam under 70 bar (= 0.28 t of steam/t of oil) in a static mixer and then atomized with 8,050 m3 (S.T.P.)/h of oxygen, with which 0.5 t/h of steam has been mixed (0.05 t of steam/t of oil), and reacted at 1400C. After cooling, the cleavage gas has a CO2 content of 5.4% and a carbon black content of 1.9 kg of carbon per 100 g of ~tarting oil (Point 1 in Figure 2).
EXAMPLE ~
In a synthesis gas generator operated under the same conditions a~ in Example 1, 10 t/h of vacuum residue are introduced but the oil is predispersed with a larger amount of 3.91 t of steam under 70 bar, ie. 0.39 t of steam/t of oil, and reacted with a corre~pondingly larger 2 ~ ~ 9~ ~
- 7 - O.Z. 0050/40532 amount of oxygen, with which 0.5 t/h of qteam is likewise mixed. The cooled cleavage gas contains 7.1~ of C2 and 1.17 kg of carbon per 100 g of ~tarting oil (Point 2 in Figure~2). It can be seen that higher CO2 values, due to more steam and more oxygen, give rise to lower carbon black value~ at the same load.

12.5 t/h of vacuum residue are gasified under the same conditions as in Example~ 1 and 2, ie. at a 25%
higher load and with the same nozzle arrangement. The oil is predispersed as in Example 2, with 4.8 t/h of steam under 70 bar, ie. more than 0.39 t of steam/t of oil, and then gasified with 10,000 m3 (S.T.P.)/h of oxy-gen with which 0.4 t/h of steam has been mixed. The cooled cleavage gas contains 7.1% of C02 and 0.8 kg of carbon per 100 kg of oil used (Point 3, Figure 1). It can be ~een that the higher load results in an increase in the quality of ga~ification with otherwise identical proce0s parameters.

In the 3ame synthesis gas generator as that used in Example 1, a nozzle according to Figure 1 is in-stalled. The orifice of the steam nozzle ends 2 mm, in the direction of flow, before the oil pipe connection.
The steam pressure before the nozzle i~ 100 bar, ie. 2.5 times the reactor pressure, which corresponds to about 135% of the crit.ical pre~ure difference. 10 t~h of vacuum residue are gasified with 2.66 t/h of steam vla the nozzle (0.27 t of steam/t of oil) with the addition of ~,900 m3/h of oxygen, to which a further 1.1 t of steam (0.11 t of steam/t of oil) are added.
The cooled cleavage gas contain~ 4.2% of CO2 and 0.25 k~ of carbon in the carbon black per 100 kg of oil u~ed (Point 4 in Figure 2). It can be seen that a con-siderably smaller amount of carbon black i~ formed with substantially lower CO2 value~. In thi~ case, the carbon black contain~ 214 of slag, ie. there are only 3.8 kg of 20~9~:~
- 8 - o.Z. 0050/40532 carbon per kg of slag whereas in Example~ 1 to 3 about 15-25 kg of carbon were obtained per kg of ~lag. Re-cycling of carbon black can be dispensed with.

S Under the same conditions as in Example 4, 10.5 t of ~acuum residue are ga~ified while pas~ing the same amount of ~team through the nozzle, ie. 2.64 t/h of steam under 100 bar. The amount of ~team, based on the oxygen, i8 slightly reduced to 1.0 t/h, ie. 0.09 t of steam/t of oil.
After cooling, the cleavage gas contains 3.5% of CO2 and 0.42 kg of carbon black per 100 kg of oil. Point 5 in Figure 2 shows th~t the use of le88 steam and oxygen leads to smaller amounts of CO2 and larger amounts of carbon black.

Under conditions otherwise identical to those in Examples 4 and 5, 7 t/h of vacuum residue ~30% le88 ) are gasified with a correspondinqly smaller amount of oxygen, to which an amount of only 0.08 t of steam (= 0.01 t of steam/t of oil) i3 added. This means that the entire amount of moderating steam of 2.64 t/h, ie. 0.38 t of steam/t of oil (as in Examples 2 and 3), i8 let down via the nozzle. These gasification conditions are 80 advan-tageous that it is po~sible to manage with a smaller specific amount of oxygen than in Examples 2 and 3. The cooled cleavage gas contains 6~ of CO2 and 0.25% of carbon in the carbon black per 100 kg of oil used (Point 6 in Figure 2). It can be seen that the larger specific amount of ~team per t of oil, resulting from the constant amount of ~team at a fixed nozzle cross-section with a partial oil load (-30%), gives rise to the formation of more CO2, but that, owing to the substantially better quality of ga~ification when the novel procQss i8 used, an extremely ~mall amount of carbon result~ in the gas.

Claims

1. A process for the preparation of a synthesis gas by partial autothermal oxidation of liquid fuels and/or solid fuels in the presence of oxygen or oxygen-containing gases with the addition of a temperature moderator, such as steam and/or CO2, in an empty reactor space without baffles, at from 1000 to 1500°C under from 1 to 100 bar, wherein the reactants fuel and oxygen-containing gas are fed separately to the reactor by feed-ing in the steam or CO2 simultaneously with the feed of the fuel and letting down the steam through one or more nozzles into the fuel stream directly before the orifice for the fuel, let-down being effected at from 30 to 250%, preferably from 80 to 140%, of the critical pressure ratio.

2. Apparatus for carrying out a process as claimed in claim 1, which comprises an empty reactor which is free of baffles and has a three-stream burner with in each case one or more separate feeds for fuel (2) and oxygen (3) to the water-cooled burner mouth (5) and parallel feeds of fuel and steam and/or carbon dioxide, the pipe for the steam (1) being laid concentrically inside the pipe for the fuel, and the steam being let down into the oil through a central nozzle which ends flush with the orifice of the fuel pipe or up to 5 times the diameter of the fuel pipe, in the direction of flow, before the said orifice, and a cooling water feed (4).

3. Apparatus as claimed in claim 2, wherein the steam pipe is laid inside or outside the fuel pipe and the steam is allowed to enter the fuel stream from an annular space around the burner pipe through from 2 to 6 orifices at an angle of from 5 to 90° to the fuel stream.

4. A process as claimed in claim 1, wherein, for full or part load, the same amount of steam is always allowed to flow out, ie. the amount is not regulated by upstream control elements, and the nozzle orifice or orifices is or are dimensioned such that, in the case of - 10 - O.Z. 0050/40532 part load, a total amount of steam required for carrying out the process flows through the nozzle and, in the case of full load, the additional amount of steam required is added to the oxygen or to the fuel.

5. Apparatus as claimed in claims 2 and 3, wherein the amount of steam is adjusted for part load by intro-ducing an adjustable conical nozzle needle into the nozzle from the rear pipe end and adjusting the orifice cross-section by the position of this conical needle in such a way that, for each load, the optimum amount of steam flows out at the pressure difference described.