WO2020201785A2

WO2020201785A2 - Improved process for production of hydrogen rich gaseous mixture

Info

Publication number: WO2020201785A2
Application number: PCT/HU2020/000013
Authority: WO
Inventors: Esa Albert KURKELA; Nieminen MATTI; Norbert BENKÖ; Bence NAGY; László Leveles
Original assignee: Mol Hungarian Oil And Gas Public Limited Company; JELINEK, István; Auer, Róbert
Priority date: 2019-03-29
Filing date: 2020-03-25
Publication date: 2020-10-08
Also published as: HUP1900101A1; WO2020201785A8; HU231257B1; WO2020201785A3

Abstract

Petroleum coke-based feed materials are catalytically gasified by steam to hydrogen rich gaseous mixtures at low pressure and moderate temperature, saving thereby investment and operational costs. Both the pressure of 3-5 bar and the temperature of 750°C applied according to the invention were found to be optimum values, below or above which reaction rates were decreased. Under the reaction conditions of the invention, in addition to the steam gasification gf the carbon content to carbon monoxide and hydrogen, water gas shift reaction with excess water takes place simultaneously, producing an additional amount of hydrogen. Based on the composition of product gases, at about 98% carbon conversion the conversion of the primary product carbon monoxide to carbon dioxide and hydrogen is about 90%. As an overall result, 1 mol carbon content of the feed is converted to about 1,8 mol hydrogen.

Description

Improved process for production of hydrogen rich gaseous mixture.

The present invention relates to the gasification of petroleum coke-based feed materials. More particularly, the invention relates to an improved process to convert petroleum coke and steam to a hydrogen rich gaseous mixture, wherein investment costs are reduced, and hydrogen yield is increased.

Petroleum coke is produced in large amounts in refinery cooker units as byproduct. Several options are known to utilize this byproduct. The simplest way is to use it as fuel, providing heat energy or electricity for various refinery processes. More attractive ways are to convert petroleum coke to value added products, such as by converting it to activated carbon, which can then be used in water or gas treatment or for the production of electrical components

Ever tightening rules and regulations impel refineries to the intensive application of hydrogenation technologies in refining processes to meet standard motor fuel requirements. Therefore, the most expedient way for a refinery for the utilization of the vast petroleum coke byproduct could be its gasification to a hydrogen rich gaseous mixture, which would at least partly cover the increasing hydrogen demand. When hydrogen is the targeted product, petroleum coke is gasified with steam according to equation (1) The product mixture, after separation, can be processed further to produce an additional amount of hydrogen by the water gas shift reaction (WGSR), equation (2):

C+H₂0 C0+H₂ (1)

C0+H₂0 C0₂+H₂ (2)

Thus, one mol of carbon can be converted to two mols of hydrogen by the two consecutive steps (1) and (2).

The theoretical product mixture of the steam gasification step (1) will contain 50 v/v% hydrogen at 100% carbon conversion, and maximum hydrogen yield can be 0,167kgH₂/kg coke. With WGSR (2) of the product mixture, the final product at 100% shift will contain 67% H₂ and 33% C0₂, and the maximum hydrogen yield with the additional mol of hydrogen will be 0,333 kgH₂/kg coke. The equilibrium of reaction (2) is affected by the temperature. At high temperatures, the equilibrium is strongly on the carbon monoxide side, while low operation temperatures favor high concentration of hydrogen and carbon dioxide. In non-catalyzed conditions, the reaction rates are fast enough to approach equilibrium only at above temperatures of 780-800 °C, while catalysts are needed at low temperatures for increasing the yield of hydrogen.

Thermal gasification of carbonaceous materials including petroleum coke is a well- known technology. The gasification reaction is performed either thermally or catalytically. Petroleum coke has a low volatile matter content and a low gasification reactivity. That is why, very high temperatures (1300-1600°C) are required in thermal gasification to achieve nearly complete (95-98%) carbon conversion. Required gasification temperatures can only be achieved by autothermal gasification with high oxygen feed rates. In order to reach even satisfactory energy efficiency, very little or no steam are used in these high-temperature gasifiers and thus the WGSR reaction (2) plays only a minor role, while the gasification process is dominated by reactions (3) and (4).

C+0₂ C0₂ (3)

C+C02<®2 CO (4)

The hydrogen contents of present art high-temperature gasifiers in most cases are 30% or less even if a water quench is used to cool the gas. Thus, a large secondary catalytic shift conversion unit with additional steam feeding is required to increase the hydrogen yield.

Catalytic gasification can be performed at significantly lower temperatures (650- 800°C). Catalysts used contain alkali metal hydroxides or carbonates or their mixture, at a relatively high ratio of 5-20%. Pressures applied are usually elevated pressures, especially when methane is the targeted product (40-70 bar). For thermal gasification lower pressures (1-5 bar) are also applied, but at least 1300°C is required.

US 4332641 presents a method to produce a ..hydrogen rich synthesis gas”, wherein the concentration of the hydrogen is 55%, by thermally steam gasifying coke that was prior oxidized by air. This method is, however, only a partial gasification as only 15% of carbon is gasified at 1400-1600°C, while most of the carbon ends to the coke residue, which is then used as a low sulfur coke. EP 0024792 targets“methane lean synthesis gas” in a catalytic gasification. Mild conditions are used to avoid methane formation, which is considered as byproduct. The parameters that are critical in methane formation are temperature, pressure and steam to coke ratio. At 650-790°C and 1 ,75-14 bar, preferably at 3.5-14 bar, using 0,3- 0,8 part steam per part coke, methane formation was below 2%, and hydrogen content of the synthesis gas was 49,5%. Water gas shift reaction (2) followed in a second reaction step, when, after the separation of carbon dioxide from the hydrogen - carbon dioxide mixture, hydrogen with 97% purity was obtained. According to the experiments carried out to support the present invention, the suggested operating conditions of EP0024792 do not result in optimal conversion of pet-coke carbon. The pressure range of 3.5-14 is already too high to reach optimal reaction rate and the used ratio of steam and pet-coke carbon is far too low to reach maximum hb yields. Thus, a secondary catalytic conversion step, WGSR, is needed in the process that results in additional investment and operational cost.

It is an overall object of the present invention to provide a process for the gasification of petroleum coke-based materials to hydrogen rich gaseous mixtures, that process has low investment and operational costs.

It is a particular object of the present invention to operate said gasification at conditions, which are energetically reasonable and, at the same time, offer the highest reaction rates.

It is another particular object of the present invention to obtain a hydrogen rich gaseous mixture product from a single step gasification reaction, without separate catalytic water gas shift reactor, that product mixture contains more than 50% hydrogen, preferably more than 60% hydrogen

The inventors have found, that in catalytic steam gasification, petroleum coke-based feed materials show the highest reaction rates at 740-750°C and in the 3-5 bar range, preferably at 3-3.5 bar. Above the 3-5 bar pressure range, product CO exerts an inhibitive effect on the catalyst, also decreasing the catalytic activity, the higher the pressure the higher the inhibitive effect. Above 750°C, the alkali catalyst compounds start to sinter, the alkali metal ion component of the catalyst is partially reduced to metal under the reductive conditions of the gasification reaction and evaporates, resulting in the reduction of the catalytic activity. The inventors have furthermore unexpectedly found, that when catalytic gasification is processed at the optimal parameters as said above in the presence of excess steam sufficient for the shift reaction, water gas shift reaction (equation 2) takes place with high conversion, simultaneously with the first gasification reaction (equation 1), so that both reactions are simultaneously performed during initial coke gasification. The concentrations of H2, CO2, CO and H2O correspond to equilibrium of reactions (2) calculated at 60-150 °C lower temperature than the temperature of the product gas leaving the gasifier. The hydrogen content of the product gas after the gasifier is 60- 70% (in dry gas), that drops to 53-60% when oxygen is fed with the steam. The rest of the product gas is CO2, residual CO and minor amount of methane (below 1.5). In the process of the invention the raw gas leaving the recycling cyclone of the gasifier is cooled to 300-500 °C and filtered from particulate matter. If the target product is hydrogen, the filtered gas is led directly to the hydrogen separation unit.

As used in this disclosure,“petroleum coke-based feed material” refers to a feedstock, which is a mixture of 70-100% petroleum coke and 0-30% of other carbonaceous material(s), which additional carbonaceous material is one or more of biomass, coal, waste-based fuel or petroleum heavy residue.

As used herein,“hydrogen rich gaseous products” or“hydrogen rich gaseous mixture” refer to a mixture of gases obtained by the steam gasification of petroleum coke-based feed materials, that contain at least 53 v/v% hydrogen, 0-5 v/v% carbon monoxide, 20- 30 v/v% carbon dioxide and 0-2% methane.

One possible embodiment of the invention is illustrated in Figure 1. Petroleum coke- based feedstock is comminuted over 90% to particulate sizes of 0-5 mm, preferably to 0.5-2 mm, fed into an industrial mixing-drying device, and impregnated with an aqueous solution of the catalyst by spraying the aqueous solution onto the mixed comminuted feed. The amount of catalyst is 5% relative to the petroleum coke-based feedstock. The impregnated solids are then dried at ambient pressure or preferably in a vacuum at ambient temperature to remove major part of the added impregnation water.

The comminuted and impregnated petroleum coke-based feedstock is fed into the bottom part of a continuously operated autothermal circulating fluidized bed gasification reactor and is reacted with a stream of steam and oxygen, optionally in the presence of an additional fluidizing gas, which can be, for example nitrogen or carbon dioxide. The gasification reactor has a recycling cyclone to separate entrained fines from product gases, which fines are recycled into the reactor. Char is withdrawn at the bottom. A small amount of a calcium- and/or magnesium-containing bed additive is fed together with the feedstock in order to contribute to the gasification and tar decomposition reactions and specially to help in avoiding ash sintering and deposit formation in the gasifier. This additive can be e.g. limestone, dolomite or magnesium- containing rock, which are crushed and screened to the desired particle size of 0 - 1 mm, preferably to 0.2-0.6 mm. The additive feed rate is adjusted to correspond to 0.5- 2 %wt. of the feed rate of the petroleum coke-based feedstock. During gasification, the bed additive is gradually grinded, and the resulting dust is elutriating from the gasifier to the filter and in this process, it also acts as an adsorbent for partly molten or volatilized alkali metals. The filtered product gas is then led into the subsequent processing steps, which may include acid gas removal, PSA for H2 separation and/or synthesis plant for making methanol, Fischer-Tropsch products or other final products. In this process, the gasification steam is effectively used in the gasifier for the simultaneously happening carbon gasification and water gas shift reaction.

Another possible embodiment of the invention is based on allo-thermal steam gasification with external heating. Heat for the endothermic gasification reaction can be provided by several known methods such as, using two parallel fluidized beds with recycling hot solids or by using heat transfer tubes in the fluidized-bed gasifier reactor. In this allo-thermal gasification case, the hydrogen content of gas is even higher than in autothermal gasification, up to 60-70 %, as lower amount of C02 originating from the combustion reaction is mixed with the hydrogen product.

The inventors have found that the steam gasification reactivity of petroleum coke at 730-750 °C can be increased from practically zero level of not catalyzed thermal gasification to 20-100 %/min when 5-10 % of sodium-or potassium containing catalyst is added to the petroleum coke. In studying the effects of pressure and gas atmosphere on the gasification reactivity, the inventors have surprisingly found, that gasification, as expressed by the amount of hydrogen produced from unit amount of petroleum coke within unit time, has a maximal value as the function of reaction pressure at as low as 3-5 bar, below and above which gasification rate, as defined above is less than at pressures within the given range. This is surprising, as pressure levels of catalytic gasification are usually within the range of 10-70 bar; the exception is EP0024792 referenced above, the object of which is to avoid methane formation, and applies mild conditions of 1 ,75 - 14 bar and 650-790°C. Gasification rate as defined above also shows maximal value as the function of temperature, the optimum being 750°C. Experimental results for the dependence of the rate of hydrogen production from pressure and temperature are presented in Table 1. These data are obtained at a bench-scale .

Table 1 Rate of hydrogen production from petroleum coke-based feeds at 1-10 bar and 700-780°C

Without wishing to be bound to any theory, the effect of the reaction pressure on hydrogen production rate in the gasification reaction of petroleum coke-based feedstocks as presented in Table 1 can be attributed to the inhibitive effect of the carbon monoxide reaction product. In laboratory scale TGA experiments we have found, that when a sample of impregnated petroleum coke was gasified in steam that contained carbon monoxide, the gasification rate was significantly slower, than with pure steam.

As for the effect of the reaction temperature, below 750°C the reaction is too slow. Above 750°C, alkali compound starts to sinter, the alkali metal ion is partially reduced to alkali metal under the reductive conditions of the gasification reaction and evaporates, resulting in the reduction of the catalytic activity.

Consequently, based upon the data of Table 1 , the preferred pressure range is 3-5 bar, the preferred temperature is 750°C for the catalytic gasification of petroleum coke- based feed materials.

Unexpectedly, under the said preferred reaction conditions and applying steam in at least two-fold molar excess to coke, which requires a steam/coke weight ratio of at least 3, the gasification reaction of the carbon (equation 1) and the shift reaction of the gasification product CO (equation 2) proceed simultaneously. Characteristic product slate is 68-70% hydrogen, 2-5% carbon monoxide, 26-30% carbon dioxide, and 0,3- 0,7% methane, while when oxygen is also fed is 53-60% hydrogen, 2-13% carbon monoxide, 26-32% carbon dioxide, and 0,3-1% methane. This indicates, that in the presence of excess steam and under the preferred conditions of the invention, product CO enters rather efficiently in the shift reaction with excess steam producing additional hydrogen. Practically no methane is produced by gasification reactions, while the small methane content corresponds to 30-50% of the volatile matter present in petcoke. Product gases are cooled, and the hydrogen content may be separated by any method known in the art, such as pressure swing adsorption. Hydrogen of 97-99% purity can be obtained.

The catalyst can be regenerated by washing the char withdrawn from one or more of the sources: the bottom of the reactor, the cyclone and from the filter dust. The char is placed into a suitable extraction device known in the art, for example in a Soxhlet extractor, and extracted with water under mild conditions for several hours. Makeup catalyst is dissolved in the resulting solution, and this is then the aqueous solution that is used to impregnate the fresh feed as described above. 85-90% of the alkali catalyst compound can be recovered.

According to the above the invention relates to a process for the catalytic gasification of petroleum coke based feed materials to a hydrogen rich gaseous product mixture, comprising: providing a petroleum coke-based feed material; particulation of said petroleum coke-based feed material over 90% to 0,5-5 mm particle sizes; impregnation of the comminuted feed material with an aqueous solution of one or more compounds that are suitable to catalyze gasification reaction; feeding the particulated and catalyzed feed material into a gasification reactor; gasification of the feed material with steam to obtain a hydrogen rich gaseous product mixture, characterized by that

a) the pressure in the gasification reactor is set to 3-5 bar;

b) the temperature in the gasification reactor is set to 740-750°C;

c) the steam to coke molar ratio in the gasification reactor is at least 2, the weight ratio is at least 3.

Preferably the gasification of the carbon content of the feed material to carbon monoxide and hydrogen, and the water gas shift reaction of the gasification product carbon monoxide to carbon dioxide and additional hydrogen, proceed simultaneously. At 97-98% carbon conversion in the gasification reaction the water gas shift reaction reaches at least 85% conversion, preferably at least 90% conversion, while side reaction of carbon monoxide with hydrogen to methane is below 1 %.

The gaseous product mixture of the gasification contains at least 60% hydrogen, more preferably the gaseous product mixture contains 68-70% hydrogen, and the hydrogen production rate is at least 16,00g H2/kg coke/min. Carbon gasification and water gas shift reactions proceed simultaneously and 1 mol carbon content of the feed is converted to at least 1 ,85 mol hydrogen in one reactor by one single pass; The petroleum coke-based feed material according to the invention contains 70-100% petroleum coke and 0-30% of other carbonaceous materials, which can be one or more of biomass, coal, waste-based fuel, heavy petroleum residue and the likes;

The gasification reactor used is preferably a circulating fluid bed reactor.

As the compounds that catalyse gasification alkali metal or alkaline earth metal compounds; such as one or more of sodium, potassium, calcium and magnesium, and as anion one or more of hydroxide, carbonate, sulphate, nitrate and chloride may be used.

By applying the method of the invention, hydrogen production efficiency has been significantly increased, while investment costs have been significantly reduced, as compared to the methods of the present art.

®At the pressure level chosen, the inhibiting effect of product CO on catalytic gasification does not occur or is minimal.

-* Consequently, with all other parameters fixed, highest gasification rates can be achieved at pressures of as low as 3-5 bar, which results in reduced investment costs.

® The temperature level chosen is high enough for a reasonable gasification rate, but too low for causing catalyst deactivation by sintering and evaporation, which may occur only at a minimal level.

® Under the reaction conditions of the invention, and in the presence of excess steam, gasification of feed carbon and the water gas shift reaction of the gasification product carbon monoxide proceed simultaneously, with 97-98% carbon conversion to carbon monoxide and hydrogen, and about 90% carbon monoxide conversion to carbon dioxide and additional hydrogen.

-» Consequently, one mol carbon content of the carbonaceous feedstock is converted approximately to 1 ,9mol hydrogen in one single pass, and thus there is no need for a second water gas shift reactor to convert carbon monoxide to additional hydrogen - Carbon monoxide reacts in the water gas shift reaction with high selectivity, side reaction to methane that consumes the desired product hydrogen is minimal.

Further details of the invention are given in the examples without to restrict the invention to the examples. Example 1. Char gasification reactivity of original pet-coke and impregnated pet-coke.

The reaction rate of original pet-coke and impregnated pet-cokes were extensively studied at a pressurized thermo-balance. Table 1 shows typical data obtained for original pet-coke and pet-coke impregnated with 5-7 % of K2C03. These data are measured in a synthetic gas mixture consisting of 50 % steam, 30 % H2, 10 % CO and 10 % N2 as the steam gasification reaction is inhibited by the product gas component H2 and CO and thus this measurement corresponds better to the reaction rate in real gasifiers that tests under 100 % steam.

The reaction rate had a maximum at around 3 bar, and it was significantly lower at atmospheric pressure as well as at 10 bar. The resulting ash after thermo-balance gasification was examined under microscope and it could be noticed that at all tests carried out at above 750 °C the catalyst material sintered or completely melted, which could be seen as dramatically decreased reactivity. The sintering and melting tendency were more severe at higher operation pressures for example at 10 bar than at pressures of 1-3 bar. At 10 bar sintering took place already at 750 °C.

Table 1. Thermo-balance reactivity results.

* = not relevant as the catalyst sinters and melts completely at > 760 °C

Example 2. The performance of an industrial pilot plant estimated by engineering process modell

Based on the obtained laboratory reaction data and performed bench-scale fluidized- bed gasification tests a process model was made to estimate the performance of an industrial pilot plant. At this plant, petroleum coke is comminuted over 90% to 0,5-2 mm particulate sizes. The comminuted coke is fed into an industrial mixer-dryer system, where it is impregnated with the aqueous solution of potassium carbonate so that the impregnated coke contains 5% potassium carbonate. Comminuted and impregnated petroleum coke is then fed into a continuously operated circulating fluidized bed reactor at a rate of 111 ,7 kg/h and is fluidized with 334 kg/h steam and 68,4 kg/h oxygen. Steam to coke weight ratio is 3, molar ratio is 2. The temperature of the bed is 750°C, reactor pressure is 3 bar. Product gases are led through a cyclone, where entrained fines are separated and recycled. The gaseous mixture contains 53-60% hydrogen, 2- 13% carbon monoxide, 26-32% carbon dioxide, and 0,3-1 % methane. The gaseous product mixture can be optionally separated by pressure swing adsorption.

Carbon conversion is 97-98%, hydrogen production rate is 17,283 gH2/kg coke/min.

Claims

What we claim is:

1. Process for catalytic gasification of petroleum coke-based feed materials to a hydrogen rich gaseous product mixture, comprising: providing a petroleum coke- based feed material; particulation of said petroleum coke based feed material over 90% to 0,5-5 mm particle sizes; impregnation of the comminuted feed material with an aqueous solution of one or more compounds that are suitable to catalyze gasification reaction; feeding the particulated and catalyzed feed material into a gasification reactor; gasification of the feed material with steam to obtain a hydrogen rich gaseous product mixture, characterized by that

a) the pressure in the gasification reactor is set to 3-5 bar;

b) the temperature in the gasification reactor is set to 730-750°C;

2. Process of claim 1 , wherein the gasification of the carbon content of the feed material to carbon monoxide and hydrogen, and the water gas shift reaction of the gasification product carbon monoxide to carbon dioxide and additional hydrogen, proceed simultaneously.

3. Process of claims 1-2, wherein the gaseous product mixture of the gasification contains at least 53%, preferably 60-70% hydrogen already in the gasifier.

4. Process of claims 1-3, wherein the gaseous product mixture contains 60-70% hydrogen, and the hydrogen production rate is at least 16,00g h /kg coke/min.

5. Process of claims 1-4, wherein carbon gasification and water gas shift reaction proceed simultaneously and 1 mol carbon content of the feed is converted to at least 1,85 mol hydrogen in one reactor by one single pass.

6. Process of claim 1 , wherein petroleum coke-based feed material contains 70-100% petroleum coke and 0-30% of other carbonaceous materials, which can be one or more of biomass, coal, municipal solid waste, heavy petroleum residue and the likes.

7. Process of claim 1 , wherein the gasification reactor is a circulating fluid bed reactor.

8. Process of claim 1 , wherein the compounds that catalyse gasification are alkali metal or alkaline earth metal compounds.

9. Process of claim 8, wherein the alkali metal and the alkaline earth metal is one or more of sodium, potassium, calcium and magnesium, and the anion is one or more of hydroxide, carbonate, sulphate, nitrate and chloride.

10. Process of claim 1 , wherein:

a. a calcium- and/or magnesium-based bed additive is used in the gasifier, and

b. the product gas is cooled to 300-500 °C and then filtered from the particulate matter.

11. Process of claim 1 , wherein the ash streams of the gasifier are washed, and the recovered catalyst is recycled back to the impregnation process.