WO2025027431A1

WO2025027431A1 - Biogas upgrading system

Info

Publication number: WO2025027431A1
Application number: PCT/IB2024/056915
Authority: WO
Inventors: Flavio MANENTI
Original assignee: Politecnico di Milano
Current assignee: Politecnico di Milano
Priority date: 2023-08-01
Filing date: 2024-07-17
Publication date: 2025-02-06
Anticipated expiration: 2026-02-01
Also published as: IT202300016320A1

Abstract

The present invention relates to a biogas upgrading system, and plants comprising said system.

Description

BIOGAS UPGRADING SYSTEM

The upgrading of biomethane biogas is a technology of great interest both nationally and internationally : it allows to produce biomethane, which can be used as an alternative to fossil methane, starting from a renewable energy resource (biogas ) for example generated by water treatment plants , from wet waste fraction and many other wastes of industrial and agricultural origin .

The biogas produced by the anaerobic digestion from water treatment sludge has great potential to reduce the use of fossil fuel : once appropriately processed and converted into biomethane through an " upgrading" process , it can be used for example as a biofuel for the automotive industry or introduced into the natural gas distribution network .

The biogas produced by the anaerobic digestion from water treatment sludge is a gas mixture which mainly contains (Moretta et al . , 2022 ) :

- Methane (biomethane ) at 45-65%v

- CO2 at 35-55%v

- Typically oxygen up to 1 . 5%v

- Impurities such as H2S, NH3 etc . besides moisture .

The high methane content in the biogas resulting from said anaerobic digestion processes does not allow to use it as a widespread energy carrier . Furthermore, the high CO2 content does not allow to introduce methane into the public supply system or to use it as methane for the automotive industry .

The technological evolution of CO2 extraction treatments has made the use of transformation of biogas into biomethane, through a process referred to as " upgrading" , cost-effective . The biogas " upgrading" process , which mainly consists in removing carbon dioxide and other impurities , allows to produce biomethane .

There are various technologies for separating CO2 from a gas mix . The choice of the technology to be used depends on the purity required for the product and the conditions of the gas to be treated (temperature, pressure, impurities present or concentration of CO2 in the gas ) .

In the current biomethane plants , the biogas is compressed and separated into its two main components : biomethane and carbon dioxide . Biomethane is introduced into the gas supply network, while the flow of carbon dioxide is released into the atmosphere or it is introduced into cylinders for use as inert in some industrial sectors .

The current biogas and biomethane production plants operate according to the block flow diagram of Figure 1 . Agricultural and/or food wastes , the sludge from animal faeces or the organic fraction of municipal solid waste are digested anaerobically in a digester . Anaerobic digestion generates biogas (Moretta et al . , 2022 ) , that is a current process . Such current , also referred to as crude biogas , is sent to a f iltering/washing system for reducing the impurities and subsequently :

- to a generation motor, in the case of conventional biogas plants (Figure 2 ) ;

- to a biogas upgrading system, in the case of biomethane production plants (Figure 3 ) .

The biogas upgrading system mainly consists of :

- a compression unit ;

- a splitting unit , and

- a thermal exchange system .

In particular, the membrane-based upgrading technique is widely used .

Purified from impurities , crude biogas becomes biogas in this manner .

Biogas is compressed up to 8 bar, preferably up to at least 15 bar (two compression stages ) . The compression system is often provided with a dehumidifier, except for the cases of dry biogas or upstream dehumidification . Following the compression, the biogas heats and the temperature should be preferably corrected .

The compressed biogas is sent to the membrane-based system which carries out the splitting between methane and carbon dioxide .

The methane is further compressed (third stage, at times even fourth stage based on the pressure drops astride the membranebased system) up to beyond 60 bar, that is up to a pressure useful for its injection into the natural gas distribution network and its temperature is corrected once again .

Carbon dioxide is released into the atmosphere after lamination .

There are various splitting techniques such as for example amine washing, water washing, scrubbing, absorption and adsorption systems , abatement with ionic liquids and generally with softening systems . For each of these, the third compression stage for introduction into the network is still necessary .

In the case of biomethane liquefaction plants , the concept does not change, given that the liquefaction is carried out through compression, cooling and expansion until the methane (and, therefore, biomethane ) cryogenic storage conditions (- 142 ° C and 4 bar) are reached .

A particularly critical aspect of the current plant s lies in the high cost with respect to the production volume . In the case of biogas upgrading, the costs of the plant become a major factor and for the biogas market it is important to have cost-effective, non-pollutant , safe and low thermal budget technologies .

Advantageously, the present invention overcomes the problem relating to high ( investment , operating and maintenance ) costs , minimising the size of the conversion plant ; furthermore, the present invention advantageously minimises the residual emissions of carbon dioxide (eliminating them in an embodiment ) .

Advantageously, the present invention also allows to obtain an excellent conversion of biogas into biomethanol.

DESCRIPTION OF THE FIGURES

Figure 1: Block Flow Diagram (BFD) of a plant for producing biomethane from biogas:

1: agri-food residues sludge treatment (MSW)

2 : biogas plant

3: digested fertilizers

4 : biogas

5: Upgrading biogas

6: CO2

7 : biomethane

Figure 2 : Main operations for a conventional biogas plant for producing electrical energy:

8: agri-food residues sludge treatment (MSW)

9: anaerobic digestion

10: digested fertilizers

11: crude biogas

12 : blower

13: crude biogas

14 : filters

15: biogas

16: heat exchanger

17 : biogas

18 : machine

19: CO2 and steam to atmosphere

20 : energy

21: electrical energy supply network

Figure 3: Main operations for a biomethane biogas upgrading plant :

22 : agri-food residues sludge treatment (MSW)

23: anaerobic digestion

24: digested fertilizers

25: crude biogas

26: blower 27 : crude biogas

28 : filters 29: biogas

30: compressor (2 stages)

31 : biogas

32 : heat exchanger

33: biogas

34: splitting (membranes)

35: CO2 to atmosphere

36: biomethane

37: compressor (third stage) 38 : biomethane

39: heat exchanger

40: biomethane

41: network gas (SNAM) .

Figure 4 : BFD of the present invention: 42 : agri-food residues sludge treatment (MSW) 43: biogas plant 44: digested fertilizers 45: biogas 46: upgrading biogas 47 : Residual CO2 48: SN ratio CO2 49: biomethane 50: subject of the invention 51 : biomethanol

Figure 5 : Main operations of the present invention highlighting the new units (67, 74, 76) to be inserted ex novo into a biomethane plant : 52 : agri-food residues sludge treatment (MSW)

53: anaerobic digestion 54 : digested fertilizers 55: crude biogas 56: blower 57 : crude biogas 58 : filters 59: biogas 60: compressor (2 stages) 61 : biogas 62 : heat exchanger 63 : biogas 64: splitting (membranes) 65 : CO2 to atmosphere 66: biomethane 67 : reformer 68 : use of CO2 69: rich syngas

70: compressor (third stage) 71: conditioned syngas 72: heat exchanger 73: conditioned syngas 74: methanol synthesis 75: biomethanol and water 76: separation 77 : biomethanol 78: H2O make-up 79: biomethanol water

80: Distribution and storage of biomethanol

Figure 6: Two-step option for full recovery of wastewater by reforming methanol: 81: biomethane 82 : water 83 : reformer 84: syngas 85: water/methanol from purification 86: pump/heating 87 : methanol reformer 88: condensation/separation 89: water to make-up 90 : syngas .

Figure 7 : Diagram of the reaction section with single shell units. The tube bundles of the catalytic reactors are necessarily vertical: 91 : syngas 92 : single shell heater 93: deflector 94 : single shell reactor 95: single shell cooling device 96: syngas 97 : syngas 98 : methanol water 99: methanol water 100: syngas 101: methanol water

Figure 8 : Layout for the embodiment "Biomethane and biomethanol upgrading plant with one-step reforming and two conversion stages": 102 : biogas 103: HP biomethane 104: reforming steam 105: SR OUT 106: H2O make-up 107: fresh syngas 108: CO2 to mixing 109: CO2 purging 110: syngas recycling 111: methanol synthesis 112: methanol crude 1 113: methanol synthesis 114 : purging 115: methanol crude 2 116: methanol 117: H2O 118: methanol and water recycling 119: off-gas

Figure 9 and Figure 10: data relating to the implementation Layout of Figure 8.

Below is the detailed description of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a biomethane to biomethanol upgrading system, said system comprising

- A compression unit (60) ;

- A splitting unit (64) ;

- A heat exchange unit (62) ; characterised in that said biomethane upgrading system comprises

- A reforming unit (67) arranged after said splitting unit to form syngas (synthesis gas) , wherein the reactions below are carried out in said reforming unit:

[Rl] : CH4 + H2O = CO + 3H2;

[R3] : CH3OH + H2O = CO2 + 3H2;

- The dosage of CO2 to obtain a value of SN (the excellent ratio of the molar fraction of hydrogen with respect to the sum of molar fractions of CO and CO2 for the synthesis of methanol and its derivatives (Bozzano and Manenti, 2016) )

(wherein [R2] SN = (H2 - CO2) / (CO + CO2) greater than 2, preferably comprised in the range 2<SN<2.1, even more preferably comprised in the range 2.01^SN<2.05 and however relating to the selectivity of the selected catalyst;

- Compression of the syngas (70) exiting from said reforming unit with said compression unit up to a pressure > 60 bar, preferably at a pressure comprised in the range from 60-80 bar and more preferably at a pressure comprised in the range from 60-70 bar;

- a thermal exchange (72) in said heat exchange unit

- Biomethanol synthesis (74) at o a pressure <100 bar, preferably <80 and more preferably <70 bar; o at a temperature comprised in the range from 230- 280 ° C, preferably comprised in the range from 240- 270 ° C, even more preferably from 245-260 ° C; o preferably with a heterogeneous and tubular catalytic bed .

- purification and separation ( 76 ) of biomethanol and water with recycling of the current containing residual methanol, water and superior alcohols to said reforming unit .

Preferably, the outflow of the biomethane exiting from said splitting unit ( 64 ) is comprised in the range from 15-25 bar, even more preferably between 20-25 bar .

Preferably, in said reforming unit ( 67 ) , said reaction [R3 ] is carried out with two steps comprising the following steps :

- Pumping in said reforming unit a recycling current deriving from said purification and separation consisting of o water comprised in the range from 50-100% mol, preferably 80-100%mol, even more preferably 85- 100%mol ; o biomethanol comprised in the range from 0-50%mol, preferably 0-20%mol, even more preferably 0- 0 . 15%mol, at a pressure equal to or greater than said reforming unit (typically 20 bar) . and vaporised and heated to a temperature up to 280 ° C, preferably up to 300 ° C;

- carrying out the reaction [R3 ] in a catalytic system . Said catalytic system is selected from the group consisting of : at least one catalytic bed, at least one methanol cell and/or combinations thereof .

Even more preferably, the effluents coming from said reforming unit are sent to a phase separator, wherein : - the remaining water condenses by lamination and/or heat exchange ; and

- the syngas is sent downstream of the reforming unit and mixed with syngas flowing out from said reforming unit .

Preferably, in said reforming unit ( 67 ) , said reaction [R3 ] is carried out in a single step comprising the pumping, upstream of the reforming unit , a recycling current derived from said purification and separation consisting of

- water comprised in the range from 50-100%mol, preferably 80-100%mol, even more preferably 99 . 85-100%mol;

- biomethanol comprised in the range from 0-50%mol, preferably 0-20%mol, even more preferably 0-0 . 15%mol, and mixed with replenishing water .

In this preferable embodiment (Figure 8 ) , considering the installation simplifications , the methane reforming reaction [Rl ] is slightly inhibited by the methane reforming reaction [R3 ] .

In an alternative embodiment , it is possible to exploit the convective section of the firebox of the biomethane reforming unit to carry out the methanol reforming operation according to the energy supplementation methods known to the person skilled in the art .

Advantageously, as reported above, the present invention exploits the operations already present in the biomethane production plant s to the uttermost , significantly reducing the CAPEX .

The present invention converts the whole biomethane current and part of the C02 current , otherwise released to the atmosphere, into biomethanol .

The present invention provides for a reforming unit (not bireforming or tri-reforming like in other technologies , for instance : Manenti, BIGSQUID, 2016 ) .

As reported above, the present invention intercepts the biomethane current and transforms it into synthesis gas ( syngas ) rich in hydrogen through a classic steam methane reforming operation according to the reaction [Rl ] reported above .

In the present invention, said current is mixed with an appropriate fraction of carbon dioxide coming from the venting line to the atmosphere, before decompression so as to obtain an SN ratio that is excellent for methanol synthesis (Bozzano and Manenti, 2016 ) . The dosage of CO2 is optimised in real time .

The present invention does not provide for any water-gas shift operation .

Advantageously, the present invention provides for recovering the secondary compressor of the biomethane process to compress the conditioned syngas up to the methanol synthesis pressure . Advantageously, the present invention provides for reutilising the thermal exchange already envisaged for biomethane, and then sending the syngas to the new units for the synthesis of methanol and purification of the methanol/water mixture . The water is then recycled to the reforming system so as to reduce the demi-water consumptions , but also to maximise the yield in methanol through syngas reconversion of the residual methanol contained in such water current and superior alcohols typically produced through parasitic reactions in the methanol synthesis .

Advantageously, as reported above, the present invention simplifies the stage by stage nature of the synthesis section by using partially shared units .

Figure 7 shows the case of three reaction stages :

- "Process" side, each reaction stage consists of three tube bundles , respectively for pre-heating, converting and cooling, and a separator for removing the methanol and water mixture .

- The "Utility" side, instead, does not depend on the number of stages and there is a single jacket for the pre-heating section, a jacket with vertical baffles for the conversion section and a single jacket for the cooling section .

The first stage is the most efficient in terms of synthesis and therefore it is to be considered as a limiting element when designing the pre-heating and cooling . On the other hand, bypasses for individually controlling the temperatures of each conversion stage are provided for the conversion section . Advantageously, the purification is significantly reduced with respect to a common methanol synthesis process ( for example, the purification sections were accurately described by Douglas and Hoadley ( 2006 ) ) .

Preferably, said purification comprises two phase separators combined with only one distillation tower to reach the market specifications ( 99 . 85% of purity) .

Depending on the separator-tower-separator layout shown in Figure 8 , the wastewater is recycled upstream of the reformer for full recovery within the process . The data of the purification section are contained in the spreadsheet of the Tables of Figures 9 and 10 .

In an embodiment the present invention relates to plants comprising the biomethane to biomethanol upgrading system of the present invention .

Preferably, said plant is selected from the group consisting of : biomethane production plants , biogas production plants , biomethanol and derivatives production plants , gasification plants (biomasses , plastics , sludges , Organic Fraction of Municipal Solid Waste, other) , pyrolysis plants (biomasses , plastics , sludges , Organic Fraction of Municipal Solid Waste, other) , gas plants provided with flaring system, plants with co-presence of methane and carbon dioxide ; plants with presence of methane and exogenous carbon dioxide, methanation plant .

Advantageously, the present invention allows a morphological minimisation of the biogas conversion units , capital and operating costs .

Furthermore, the present invention has an optimisation of the reuse of C02 and the production of biomethanol and derivatives .

Advantageously, the present invention leads to environmental and energy self-sustainability .

Advantageously, the system of the present invention relates :

- ex novo to conventional biogas plants

- and by way of modernising, to plants already converted to biomethanol and derivatives (REF . ; Bozzano and Manenti, Progress in Energy and Combustion Science, 2016 ) .

Below are some non-limiting exemplifying experiment s aimed at better describing the technical aspects and advantages of the present invention .

EXAMPLES

Biomethane to biomethanol upgrading plant with

- one-step reforming and

- two conversion stages .

Figure 8 shows the process layout (the layout only shows the most significant units ) .

Table 1 shows all the data deriving from massive and energy balances obtained through detailed process simulation with the aid of AspenHysys vl l .

Embodiment A

In an embodiment , the Stream purging of the process is sent to the firebox of the reformer for partial process energy self-reliance .

Embodiment B

In an embodiment , the process is suitably electrified to provide pure hydrogen and oxygen ( for example using a SOEC; Bisotti and Manenti, 2022 ) to the firebox for full energy self-reliance .

Embodiment C

In an embodiment , the process is suitably electrified also for electrical energy to all electrified machines . Embodiment D

In an embodiment , the process is suitably electrified also to provide additional hydrogen to recover all the residual CO2 according to Stream 11 of the Table achieving the total carbon negative goal .

Embodiment E

In a particular embodiment , the present invention consists of at least two plants for the synthesis of methanol and/or its derivatives from biogas / biomethane / scrap/ waste, consisting of :

- a filtering / cleaning / pretreatment section,

- a thermal or catalytic treatment section including compression - a synthesis section with possible further compres sion and storage and

- a single purification section with said purification section suitably oversized to receive multiple streams (at least two) of methanol and/or derivatives not to specification coming from an equal number of synthesis distributed on the area and with said section located in third position, preferably barycentric, with respect to such synthesis plants or at only one of them, and it is capable of generating a waste current , mainly aqueous , to be recycled to the original synthesis plants for its complete reconversion and obtaining a zeroresidue circular process network .

The transfer of the stream of methanol or derivatives not to specification and the waste aqueous mixture is carried out through road, railway or sea/river transport , preferably creating a tight network around the purification centre . Such purification centre may also in turn convert methanol into derivatives such as , by way of non-limiting example, dimethyl ether, acetic acid, propionic acid, hydrogen . In the case of hydrogen, the carbon dioxide generated is in turn recycled upstream of the original plants , where useful for the further reconversion to methanol and derivatives or reused locally for efficient carbon sink syntheses , such as for example acetic acid .

With reference to Figure 8 , the streams are therefore to be considered transported by road, railway or sea and the purification section is to be considered suitably oversized depending on the number of plants to be received .

Claims

1) Biomethane to biomethanol upgrading system, said upgrading system comprising

- A compression unit (60) ;

- A splitting unit (64) ;

- A heat exchange unit (62) ; characterised in that said biomethane to biomethanol upgrading system comprises

- A reforming unit (67) arranged downstream of said splitting unit to form syngas, wherein in said reforming unit there are carried out the reactions below:

[Rl] : CH4 + H2O = CO + 3H2;

[R3] : CH3OH + H2O = CO2 + 3H2;

- The dosage of CO2 deriving from said splitting unit to obtain a value of SN greater than 2;

- Compression of the syngas (70) exiting from said reforming unit with said compression unit up to a pressure 1 60 bar;

- a thermal exchange (72) in said heat exchange unit

- Biomethanol synthesis (74) at o a pressure <100 bar; o at a temperature comprised in the range from 230- 280°C;

- purification and separation of biomethanol (76) and water with recycling:

- of the water current to said reforming unit and

- residual methanol and superior alcohols.

2) Biomethane to biomethanol upgrading system according to claim 1 wherein the outflow of biomethane exiting from said splitting unit is comprised in the range from 15-25 bar, preferably between 20-25 bar.

3) Biomethane to biomethanol upgrading system according to one or more of the preceding claims, wherein said SN value is comprised in the range from 2.00<SN<2.1, preferably 2.01<SN<2.05.

4) Biomethane to biomethanol upgrading system according to one or more of the preceding claims wherein said compression of syngas (70) exiting from said reforming unit with said compression unit is at a pressure comprised in the range from 60-70 bar.

5) Biomethane to biomethanol upgrading system according to one or more of the preceding claims, wherein said biomethanol synthesis (74) is carried out at o a pressure <70 bar; o at a temperature comprised in the range preferably from 245-260°C; o with a heterogeneous and tubular catalytic bed.

6) Biomethane to biomethanol upgrading system according to one or more of the preceding claims, wherein in said reforming unit (67) , said reaction [R3] is carried out with two steps comprises the following steps:

- pumping in said reforming unit a recycling current deriving from said purification and separation consisting of water comprised in the range from 50-100% mol, preferably 80-100%mol, even more preferably 99.85- 100%mol; o biomethanol comprised in the range from 0-50%mol, preferably 0-20%mol, even more preferably 0- 0.15%mol, at a pressure equal to or greater than said reforming unit and vaporised and heated at a temperature up to 280°C, preferably up to 300°C;

- carrying out the reaction [R3] in a catalytic system. ) Biomethane to biomethanol upgrading system according to claim 6 wherein the effluents coming from said reforming unit are sent to a phase separator wherein :

- the remaining water condenses by lamination and/or heat exchange ; and

8 ) Biomethane to biomethanol upgrading system according to one or more of claims 1-5 , wherein in said reforming unit ( 67 ) , said reaction [R3 ] is carried out in a single step comprising the pumping upstream of the reforming unit a recycling current derived from said purification and separation consisting of

9) Biomethane to biomethanol upgrading system according to one or more of the preceding claims , wherein said purification and separation of biomethanol and water ( 76 ) comprises two phase separators combined with a tower and said water separated in said purification step is recycled and sent upstream of said reforming system .

10 ) Plant comprising the biomethane to biomethanol upgrading system according to one or more of the preceding claims .

11 ) Plant according to claim 10 , wherein said plant is selected from the group consisting of : biomethane production plant , biogas production plant , biomethanol and derivatives production plant , gasification plant (biomasses , plastics , sludges , Organic Fraction of Municipal Solid Waste, other) , pyrolysis plant (biomasses , plastics , sludges , Organic Fraction of Municipal Solid Waste, other) , gas plants provided with flaring system, plant with co-presence of methane and carbon dioxide, plant with presence of methane and exogenous carbon dioxide, methanation plant .