The invention relates to a system and a method for generating a hydrogen rich gas from pyrolysis of carbonaceous material. The invention moreover relates to a system and a method for upgrading tar oil from pyrolysis of carbonaceous material.

Pyrolysis of carbonaceous material, such as coal or biomass, results in a pyrolysis gas which is rich in tar oil, water and a variety of hydrocarbons in vapor phase. Any contaminant, which was present in the carbonaceous material subject to pyrolysis, will be present in the pyrolysis gas. Such contaminants may present problematic issues for downstream units, e.g. poisoning issues for catalysts (if present), fouling, corrosion. Cleaning steps may be necessary in case sensitive process, equipment or catalyst are used. Tar oil has in the past been considered an undesirable by-product from pyrolysis of carbonaceous material, since there is cost and effort associated with the disposal of surplus tar. This has sparked an interest for an efficient conversion of the tar oil into products with an actual market demand.

However, upgrading or improving tar oil into valuable hydrocarbons requires a lot of hydrogen. Hydrogen is known to be obtained commercially either by methane reform- ing, methanol reforming, partial oxidation or water electrolysis. Steam reforming is very water intensive. Water is a limited resource in many geographical areas. Moreover, steam reforming catalysts are quite sensitive to poisons. To generate hydrogen from natural gas or coal is expensive, and to generate hydrogen by water electrolysis is a very expensive process providing hydrogen of a much higher purity than need for tar upgrading processes.

It is an object of the invention to provide an alternative system and an alternative method for generating a hydrogen rich gas from pyrolysis of carbonaceous material. It is moreover an object of the invention to provide an alternative system and an alternative method for upgrading tar oil from pyrolysis of carbonaceous material. As used herein, the term "pyrolysis" shall be understood as a process in which a carbonaceous feedstock, such as coal or biomass, is heated either in the absence of oxygen or in the presence of sub-stoichiometric amounts of oxygen with respect to oxidation to C0 ₂ . The products from pyrolysis consist of a solid phase, a gas phase and a liquid phase, i.e. tar oil. It should be noted that the term "pyrolysis" differs from the term "gasification" due to the temperatures in a pyrolysis and a gasification reactor differ, the water content differs and the products differ.

One aspect of the invention relates to a system for generating a hydrogen rich gas from pyrolysis of carbonaceous material. The system comprises a pyrolysis reactor arranged to carry out pyrolysis on carbonaceous material fed into the pyrolysis reactor. The pyrolysis reactor comprises a first output for outletting liquid and/or solid residue from the pyrolysis and a second output for outletting pyrolysis gas. The system moreover comprises a quenching device comprising an input for inletting the pyrolysis gas and ar- ranged to separate the pyrolysis gas into liquid effluents and off gas. The quenching unit comprises a first outlet for outletting the off gas and a second outlet for outletting liquid effluents from the quenching unit. The system moreover comprises a hydrogen generation unit arranged for generating hydrogen from the off gas by facilitating reactions of hydrocarbons in the off gas into a reformed off gas comprising carbon monox- ide and hydrogen. The system moreover comprises a gas separation unit comprising an input for inletting the reformed off gas from the hydrogen generation unit. The gas separation unit being is arranged for separating the reformed off gas into a hydrogen rich gas and a hydrogen lean gas. The system of the invention is a system where no recycle is necessary in order to obtain the required amount of hydrogen for the tar oil upgrading. Moreover, virtually no cleaning step is necessary, which provides for a less complex system, having fewer units, than a system with e.g. dedicated steam reforming equipment for hydrogen generation.

In an embodiment, the system further comprises a preheating section downstream the quenching device and upstream the hydrogen generation unit. The preheating section is arranged to preheat the off gas to a temperature in the range between about 500°C and about 800°C. The system may also comprise a heat recovery section downstream hydrogen generation unit. In an embodiment, the carbonaceous material is coal and/or biomass. In an embodiment, the liquid effluents from the quenching device comprise tar oil and/or water.

In an embodiment, the system further comprising a water gas shift section downstream the hydrogen generation unit and upstream the gas separation unit. This provides for a further generation of hydrogen.

In an embodiment, the hydrogen generation unit is a plasma unit comprising a plasma chamber, a plasma torch arranged to generate a plasma jet, a first input for inletting a torch feeding gas, a second input for inletting the off gas, a first output for outletting plasma treated gas and a second output for outletting solid and/or liquid residue. The plasma torch is arranged to provide a plasma torch having a temperature of between about 3500°C and about 5000°C. A plasma unit with a plasma torch mounted on a refractory lined reactor or chamber will be able to reform enough hydrocarbons to hydrogenate the tar oil in valuable product. The plasma chamber is empty in the sense that no catalyst is present in the plasma chamber. The lack of catalyst in the hydrogen reforming unit provides for a hydrogen generation system that is robust against poisons in the off gas.

The plasma torch is arranged to raise the gas temperature so much that the C0 ₂ present in the gas will reform the hydrocarbons present in the gas. Plasma is known to be insensitive to poisons in addition of having special properties to crack the

tars/hydrocarbons In fact, the plasma by nature dissociates the electrons from the pro- tons and creates extremely reactive radicals, boosting the cracking reactions. The plasma unit requires electricity and only minor amounts of water and air or C0 ₂ .

The plasma unit typically comprises an empty (but refractory lined) plasma reactor with a conical section at the bottom. This way the plasma reactor can be function as a cy- clone. Carbonaceous residue in the form of deposits or particles will be removed at the bottom of the reactor, by gravity through an outlet in the bottom of the reactor. The treated gas will contain less hydrocarbons (ethylene/ ethane/ propane) and more hydrogen and CO. This gas is suitable to enter a gas separation unit, such as a pressure swing absorption unit, where pure hydrogen or hydrogen rich gas is recovered. De- pending on the off gas pressure, compression of the hydrogen rich gas may also be advantageous.

In this embodiment of the system for generating a hydrogen rich gas, where the hydro- gen generation unit is a plasma unit, the system is arranged to produce hydrogen from the off gas, with virtually no cleaning step and with very limited water consumption. The system is flexible and works with a maximum load of the plasma unit of at least between 20% and 100%. The start-up of the system is easy due to the easy start-up of the plasma unit. No water gas shift unit is needed in the system with the plasma unit. However, it is possible to provide a water gas shift unit downstream the plasma unit for further generation of hydrogen.

In another embodiment, the hydrogen generation unit is a catalytic partial oxidation (CPO) unit comprising a reactor with a precious metal catalyst and optionally also a nickel based catalyst. The catalytic partial oxidation unit comprising a first input for in- letting the off gas, a second input for inletting an oxidation gas, and an output for out- letting partially oxidized gas. During operating of the system the amount of oxidation gas is adjusted so as to ensure that the temperature of the partially oxidized gas is in the range from about 700°C to about 1050°C.

This system also has a reduced water consumption compared to a system with a steam methane reforming unit. The other advantages mentioned in relation to the system with the plasma unit in relation to easy start-up, load flexibility from 20% to 100% and no need of a water gas shift unit also apply to this embodiment.

The oxidation gas to the CPO unit may be air, oxygen enriched air or pure oxygen.

In another embodiment, the hydrogen generation unit is a partial oxidation unit comprising a reactor with a reaction chamber. The catalytic partial oxidation unit comprising a first input for inletting the off gas, a second input for inletting an oxidation gas, and an output for outletting partially oxidized gas. During operating of the system the amount of oxidation gas is adjusted so as to ensure that the temperature of the partially oxidized gas is in the range from about 1200°C to about 1300°C. This system also has a reduced water consumption compared to a system with a steam methane reforming unit. The other advantages mentioned in relation to the system with the plasma unit in relation to easy start-up, load flexibility from 20% to 100%, robustness of the systems due to the lack of catalyst, as well as no need of a water gas shift unit also apply to this embodiment.

According to another aspect, the invention is also related to a system for upgrading tar oil from pyrolysis of carbonaceous material. The tar upgrading system comprises a system for generating a hydrogen rich gas according to the invention and a sub-system for improving tar oil. The system for improving tar oil comprises as least one tar hydro processing section. The system for upgrading tar oil comprises a conduit from leading hydrogen rich gas from the system for generating a hydrogen rich gas to the tar hydro processing section of the sub-system. According to this aspect the hydrogen obtained from the system for generating a hydrogen rich gas from pyrolysis is used to hydrogenate aromatic and poly-aromatic molecules in the tar oil during hydro processing. The hydrogen rich gas is led into the feedstock, viz. the tar oil, which is to undergo hydro treatment or to one or more reactors arranged for carrying out hydro processing. In case the units or units for hydro treatment comprises more than one bed of catalysts, hydrogen rich gas may be added between reactor beds, mainly for temperature control.

According to further aspects, the invention is also related to method of generating a hydrogen rich gas from pyrolysis off gas and to a method of upgrading tar oil from py- rolysis of carbonaceous material.

Objects, features and advantages of the present invention as well as presently preferred embodiments thereof will become more apparent from the description of the figures, in which:

Figure 1 is a schematic drawing of a system for generating a hydrogen rich gas from pyrolysis of carbonaceous material, and

Figure 2 is a schematic drawing of a system for upgrading tar oil from pyrolysis of carbonaceous material. The figures show non-limiting embodiments which are examples on the invention only; these embodiments are thus not intended to be limiting to the invention. Similar units and streams are denoted with similar reference numbers in the drawings. Referring to figure 1 , there is shown a schematic drawing of a system 100 for generating a hydrogen rich gas from pyrolysis of carbonaceous material.

Carbonaceous material 105, such as coal or biomass, is fed to a pyrolysis reactor 10. Pyrolysis carried out in the pyrolysis reactor 10 at a pressure close to atmospheric and at a temperature of about 550° will produce a gas 1 10 high in tars and water. However, the pyrolysis may be operated at pressures in the range from 0.1 to 5 bar atm. The pyrolysis also results in liquid and/or solid residue 1 18, which is outlet from a first output of the pyrolysis reactor. The gas 1 10 is outlet from a second outlet from the pyrolysis reactor 10.

Optionally, a cyclone unit 20 filters off a fraction of the gas 1 10, typically particles and/or solid matter within the gas 1 10, and returns the filtered off fraction 1 15 to the pyrolysis reactor 10 for further pyrolysis whilst the gas 1 10 high in tars excluding the filtered off fraction 1 15, viz. a pyrolysis gas 120, is led to a quenching unit 30.

The quenching unit 30 comprises a cooling unit 32 and a separation unit 34. The cooling unit 32 is arranged for cooling the pyrolysis gas 120 sufficiently for condensing it, so that the output stream 124 from the cooling unit 32 is a mixture of liquid and gas. In the cooling unit 32 a cooling medium is used for cooling down the pyrolysis gas 120 in or- der to provide cooling. The cooling medium is any appropriate gas or liquid, e.g. water or salt water, of an appropriate temperature. A heat exchanger may also be used for further cooling down of the pyrolysis gas. The stream 124 from the cooling unit is led into the separation unit 34 which is arranged to separate water from tar oil and gas. Three streams 126, 128 and 130 are output from the separation unit 34 and thus from quenching unit 30. These output streams are a water stream 126, a tar oil stream 128 and an off gas stream 130. The separation unit 34 may be a tank with a lower outlet for the tar oil stream 128, an outlet for the water stream 126 placed above the outlet for tar oil stream, whilst the outlet for the off gas stream is typically placed at the upper side of the separation unit 34 Typically, if 1 ton of coal is fed into the pyrolysis reactor, 0.1 ton of tar oil is output from the quenching device 30 in the tar oil stream 128. The composition of the off gas 130 depends upon the conditions, in particular the temperature, of the pyrolysis reactor 10. Exemplary compositions are given below, in a case where the carbonaceous material is coal:

Table 1 : Composition of the off gas 130 as a function of the temperature of the pyroly- sis reactor 10.

The composition of off gasses from pyrolysis of coal may e.g. be found in Dual et al., Characterization of gases and solid residues from closed system pyrolysis of peat and coal at two heating rates, Fuel, 90, 2011 ; or in Kawamura et al., Study on coal flash py- rolysis, Nippon Steel Technical report n°57, April 1993.

For temperatures of the pyrolysis reactor 10 varying from about 450°C to about 650°C, the amount of C0 _2, C ₂ H ₄ , C ₂ H ₆ and C ₃ H ₈ are highest at the lower temperatures and falls for increasing temperatures of the pyrolysis reactor 10. The amounts of H ₂ and CH4 in the pyrolysis off gas for a pyrolysis reactor 10 operating between about 450°C and about 650°C, increase with an increasing temperature. The amount of CO in the pyrolysis off gas does not vary very much with varying temperatures of the pyrolysis reactor operating between about 450°C and about 650°C. Heating value of the off gas is at its highest at about an operating temperature of about 500°C, and varies between about 5500 and 6300 kcal/m ³ , when the temperature of the pyrolysis reactor 10 varies between about 450°C to about 650°C. The off gas 130 is fed to the hydrogen generation unit 40. The hydrogen generation unit 40 may be any appropriate unit arranged for reforming hydrocarbons in the off gas 130 into a hydrogen and carbon monoxide. The hydrogen generation unit 40 may be a catalytic partial oxidation (CPO) unit, a partial oxidation (POX) unit or a plasma unit. The system 100 may further comprise a preheating section downstream the quenching device 30 and upstream the hydrogen generation unit 40. The preheating section is not shown in figure 1 or 2. The preheating unit is arranged to preheat the off gas 130 to a temperature in the range between about 500°C and about 800°C. optionally, the system 100 comprises a heat recovery section (not shown in figures 1 and 2) downstream the hydrogen generation unit 40.

Optionally, the system 100 further comprises a water gas shift section 50 downstream the hydrogen generation unit 40 and upstream a gas separation unit 60. The stream 140 from the hydrogen generation unit 40 is a reformed off gas stream, which is led to a water gas shift unit 50 for conversion of monoxide and water/steam in the reformed off gas 140 to carbon dioxide and hydrogen (H ₂ ). The output stream 150 from the water gas shift unit 50 is led to a gas separation unit 60 which is arranged for separating the reformed shifted off gas 150 into a hydrogen rich gas 160 and a hydrogen lean gas 162. In the case where the system 100 does not comprise a water gas shift section 50, reformed off gas 140' is led directly to the gas separation unit 60. This is shown by the dashed line indicated by 140' in figures 1 and 2. The gas separation unit 60 is arranged for separating the hydrogen rich gas from other components (Carbon oxides, methane, nitrogen) of the reformed off gas 140 or 140'. The gas separation unit 60 is e.g. a pres- sure swing absorption unit. A hydrogen rich gas stream 160 and a hydrogen lean gas stream 162 are output from the gas separation unit 60. The hydrogen rich gas stream 160 may be pure or almost pure hydrogen. The hydrogen lean gas stream 162 may be recycled to the pyrolysis unit, be routed to another chemical plant, be used directly or be burned off or otherwise disposed of.

As mentioned above, the hydrogen generation unit 40 may thus be a catalytic partial oxidation (CPO) unit, a partial oxidation (POX) unit or a plasma unit. These units are now described in more detail.

Plasma unit:

In one embodiment, the hydrogen generation unit 40 is a plasma unit. The plasma unit comprises a plasma chamber, a plasma torch arranged to generate a plasma jet, a first input for inletting a torch feeding gas, a second input for inletting the off gas. The plas- ma unit comprises a first output for outletting plasma treated gas and a second output for outletting solid and/or liquid residue. The plasma chamber may have a further air or steam injection input. The plasma chamber is typically an empty refractory lined reactor; that is, no catalyst material is typically present within the refractory lined plasma chamber.

The plasma torch is arranged to provide a plasma torch having a temperature of between about 3500°C and about 5000°C. Hereby, the pyrolysis off gas 130 within the plasma chamber obtains a temperature of up to 1500°C. The combination of a high temperature and the formation of very reactive radicals in the plasma region favours reforming reactions with C0 ₂ and/or H ₂ 0 if are present. The plasma unit may e.g. be a plasma unit as described in US2009077887AA.

Catalytic partial oxidation unit

In another embodiment, the hydrogen generation unit is a catalytic partial oxidation

(CPO) unit comprising a reactor with a precious metal catalyst and optionally also a nickel based catalyst. The reactor is typically refractory lined and loaded with a precious metal catalyst such as Rh or Pt supported on alumina. The refractory lined reactor may additionally contain a nickel based catalyst. The catalytic partial oxidation unit has a first input for inletting the off gas, and a second input for inletting an oxidation gas and an output for outletting partially oxidized gas. The CPO unit typically also includes a gas mixing device for mixing the off gas and the oxidation gas. During operating of the system, the amount of oxidation gas is adjusted so as to ensure that the temperature of the partially oxidized gas is in the range from about 700°C to about 1050°C. The oxidation gas is air, oxygen enriched air or pure oxygen. The CPO unit typically comprises a gas cleaning unit upstream of the CPO reactor.

The gas cleaning unit is arranged to remove poisons such as chlorine containing molecules, sulphur containing molecules, heavy metals, tars from the off gas stream entering the CPO reactor with catalyst for catalysing the CPO reaction. CPO can be used to partially oxidize a hydrocarbon into CO and H ₂ . The amount of air (or enriched air or pure 0 ₂ ) is adjusted so that oxidation reaction do not go all the way to combustion (therefore producing C0 ₂ and H ₂ 0) but are limited to CO and H ₂ .

These reactions are catalyzed by precious metals such as Rh and/or Pt. In order to ensure conversion of ethylene and ethane it is thus recommended to combine Rh with a nickel catalyst for total removal of C2+.

It has been demonstrated that a steam to carbon ratio of 0.0 is possible, which eliminates the need for steam injection. An oxygen to carbon ratio in the range from 0.2 to 0.7, corresponding to exit temperature from 700°C to 1031°C, have been proven to work well in a pilot plant.

Partial oxidation unit

In another embodiment, the generation unit is a partial oxidation (POX) unit comprising a reactor with a reaction chamber. The reactor chamber is typically an empty refractory lined reactor. The partial oxidation unit comprises a first input for inletting the off gas, a second input for inletting an oxidation gas, and an output for outletting partially oxidized gas. The POX unit moreover comprises a gas mixing device for mixing the off gas and the oxidation gas. During operating of the system, the amount of oxidation gas is adjusted so as to ensure that the temperature of the partially oxidized gas is in the range from about 1200°C to about 1300°C.

POX may be seen as the thermal version of CPO. A high temperature is reached with the injection of significant amount of air. Similar to the CPO reaction, the POX reaction conditions must favour partial oxidation conditions. Temperatures in the vicinity of 1200-1300°C are often required to get enough hydrocarbon conversion. Since no cata- lyst is present, POX is not sensitive to poisons.

Referring to Figure 2, there is shown a schematic drawing of a system 200 for upgrading tar oil from pyrolysis of carbonaceous material. The units 10, 20, 30, 32, 34, 40, 50 and 60 as well as the streams 105, 110, 115, 118, 120, 124, 126, 128, 130, 140, 140', 150, 160 and 162 of the system 100 shown in figure 1 are also part of the system 200 for upgrading tar oil from pyrolysis of carbonaceous material. The system 200 shown in figure 2 differs from the system 100 shown in figure 1 by the unit 70. The unit 70 is a tar hydro processing section. The system 200 comprises comprises a conduit from leading hydrogen rich gas 160 from the system 100 for generating a hydrogen rich gas to the tar hydro processing section 70. The tar oil stream 128 from the quench unit 30 is also led into the tar hydro processing section 70. The tar hydro processing section 70 may be a single hydro pro- cessing reactor having one or more reactor beds; alternative the tar hydro processing section may comprise more than one hydro processing reactor, each having one or more reactor beds. In both these cases, hydrogen rich gas may be added between reactor beds, mainly for temperature control. The hydrogen rich gas stream 160 is used in the tar oil upgrading unit 70 for hydrogenating aromatic and poly-aromatic molecules. From the hydro processing section 70 a hydro treated product 170 is obtained, which has low nitrogen content and a low content of aromatics. A product stream 170 in the form of an upgraded or improved tar oil stream is outlet from the unit 70.

Example:

In the following an example from the CTL (Coal to Liquid) field is given. 1 ton of coal typically provides 0.1 ton of tar oil, water and 150 Nm ³ of off gas. The composition of the off gas typically depends on the pyrolysis temperature as indicate in Table 1 above. Usually, a temperature of between about 500°C and about 550°C is the preferred pyrolysis temperature. Impurities are mainly tars, H ₂ S (between 0.1 to 0.5 mol%), metals, chlorine.

0.1 ton of tar oil requires 80 Nm ³ of pure hydrogen. In case the pyrolysis temperature is 550°C, the 150 Nm ³ off gas will only comprise 150 Nm ³ *15.49% = 23.23 Nm ³ of H ₂ (see Table 1 ). This is clearly insufficient for a proper upgrading of the tar oil without a hydrogen generation unit of the invention. In this example the hydrogen generation unit is a plasma unit. The plasma unit will carry out the following mail reactions:

C ₃ H ₈ + 1 .5 0 ₂ = 3 CO + 4 H ₂ ;

C ₃ H ₈ + 3 C0 ₂ = 6 CO + 4 H ₂ ;

C ₃ H ₈ + 3 H ₂ 0 = 3 CO + 7H ₂ ;

C ₂ H ₄ + 0 ₂ = 2 CO + 2 H ₂ ;

C ₂ H ₄ + 2 C0 ₂ = 4 CO + 2 H ₂ ;

C ₂ H ₄ + 2 H ₂ 0 = 2 CO + 4 H ₂ ;

C ₂ H ₆ + 0 ₂ = 2 CO + 3 H ₂ ; C ₂ H ₆ + 2 C0 ₂ = 4 CO + 3 H ₂ ;

C ₂ H ₆ + 2 H ₂ 0 = 2 CO + 5 H ₂ ;

2 CH ₄ + 0 ₂ = 2 CO + 4 H ₂ ;

CH ₄ + C0 ₂ = 2 CO + 2 H ₂ ;

CH ₄ + H ₂ 0 = CO + 3 H ₂

Reactions with C0 ₂ are the main target since C0 ₂ is already present in the gas, but air can be injected too to lift up the gas temperature. It is also possible to inject water or extra C0 ₂ into the plasma unit.

The following table summarizes the composition of the off gas 130 fed into the plasma unit, the air injected into the plasma unit as well as the reformed off gas outlet from the plasma unit feeds (feed gas + air) and effluent (off gas) of the plasma reactor. Feed gas is 37500 Nm ³ /h. Note that no steam has been added.

Table 2: Compositions of off gas 130 into plasma unit, air injected into plasma unit and reformed off gas 140 from plasma unit. From Table 2 it is seen that the reformed off gas 140 has 32.45 mol% H ₂ in a total output flow from the plasma unit of 61668 Nm ³ /h. This corresponds to 61668 Nm ³ /h for flow of the off gas 130 of 37500 Nm ³ /h into the plasma unit. When using a plasma unit as described, 150 Nm ³ off gas 130 fed into the plasma unit will result in 150 Nm ³ * (61668 Nm ³ /h*0.3245)/37500 Nm ³ /h = 80.0 Nm ³ H ₂ .

Thus, by using the plasma unit according to the invention for converting or reforming hydrocarbons in the off gas 130 into hydrogen, it is not even necessary to shift the gas in a water gas shift unit 50. However, if more hydrogen is needed, such a water gas shift unit may be used.

From Table 2 it is clear, that by converting all C2+, and only some of the methane, enough hydrogen can be produced. Thus, full conversion of all hydrocarbons is not needed to provide the necessary hydrogen for the tar oil upgrade.

From the foregoing description, it is apparent that there has been provided an improved system for generating a hydrogen rich gas from pyrolysis, an improved system for up- grading tar oil from pyrolysis of carbonaceous material as well as corresponding, improved methods. Variations and modifications of the herein described systems and methods within the scope of the invention will undoubtedly suggest themselves to the skilled person. Accordingly, the foregoing description should be taken as illustrative and not in a limiting sense.