A techno-economic investigation of the transition from LNG ... Ferry - A... · A techno-economic...

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A techno-economic investigation of the transition from LNG to LBG for the Samsø ferry service

Conducted By:

Naman Benday Sara Pace

Gabriel Patterson

Summer Workshop in Renewable Energy

8/20/2015

Acknowledgements: Søren Hermansen

Michael Kristensen Iva Ridjan

Rudy Garcia, Verdek LLC

Abstract: Samsø Island municipality of Denmark aspires to be fossil free by 2030. This means that coal, oil and gas for energy and transportation purposes must be phased out. In this effort, this report examines the techno-economic feasibility of transitioning the presently LNG powered ferry to a ferry run on LBG produced on the island. Various steps associated with this process, including construction of a biogas plant, upgrading facility, and cryogenic compression technology were considered. The goals of this study were to perform an economic analysis to determine the feasibility of this project based on the capital investment of 360 million DKK that Samsø made in 2014. In addition, this report sought to explore ways in which Samsø can reduce the total expenditure of the project while optimizing the output of biomethane from the island’s available feedstock. The best and most suitable bioprocessing techniques, cryogenic technologies, and high-value-adding applications of the facility’s byproducts, were investigated. Galileo Cryobox was selected as the most suitable cryogenic compression technology for the needs of this project. It was concluded that increasing the cash flow from selling coproducts from the biogas plant significantly reduces the discounted payback period and shows that a payback period of nine years could be achieved if excess LBG is sold for transportation within Samsø, digestate is sold as fertilizer, and tax benefits are included.

Samso Ferry Fuel Transition Analysis

Table of Contents 1. Introduction .............................................................................................................................................. 2

2. Methods .................................................................................................................................................... 3

2.1 Economic Analysis of LNG and LBG ..................................................................................................... 3

2.2. Biomass and Biogas Production ......................................................................................................... 3

2.3 Bioprocessing, Upgrading, and Cryogenic Technologies .................................................................... 3

3. Results ....................................................................................................................................................... 3

4. Discussion and Conclusions ...................................................................................................................... 6

4.1 Bioprocessing, Upgrading, and Cryogenic Technologies .................................................................... 6

4.2 Biomass and Biogas Production .......................................................................................................... 7

4.3 Economic Analysis ............................................................................................................................... 7

5. Recommendations .................................................................................................................................... 8

6. References ................................................................................................................................................ 9

7. Appendix ................................................................................................................................................. 10

7.1 Biomass and Biogas Production ........................................................................................................ 10

7.2 Bioprocessing, Upgrading, and Cryogenic Technologies .................................................................. 10

7.3 Economic Analysis ............................................................................................................................. 15

7.4 Literature Cited ................................................................................................................................. 17


1. Introduction Samsø Island municipality is a small cooperative sustainable community in Denmark that is

committed to a fossil fuel free island that relies entirely on renewable energy. Samsø has energy production from wind power and CHP to supply all of its electricity demands, but transportation on the island still heavily relies on fossil fuels. By 2030, the island plans to completely phase out fossil fuels used for energy and transportation. Fifty percent of the cars on the island will be electric cars by 2020 and 40-50% of local commercial transportation, including taxis, public transportation, agricultural services, and local business commuting will switch to biofuels. Further, a central focus of Samsø’s transformation includes phasing out the use of fossil fuels in its maritime ferry system. The current period poses the ferry to transition from the use of liquefied natural gas (LNG) by 2020 to on-site production of liquid biomethane by 2030. The existing ferry has a dual fuel engine that runs on imported LNG. Currently, Samsø does not have a biogas plant or gas upgrading facility established on the island for energy production, but the community has expressed deep interest in developing plans to ensure the island can produce energy from their agricultural and organic waste. Samsø intends to use the biogas produced as transportation fuel in the ferries and other vehicles after it has been upgraded to liquefied biogas (LBG).

A feasibility study and investigation into the construction of a biogas plant on Samsø was conducted in October 2014 and January 2015, respectively [1, 2]. Based on the total inventory of biomass on Samsø from the January 2015 study, the potential biogas production is approximately 5.3 million m3 per year (Table 7.1.1 in the Appendix) [2]. This data point includes 108,425 ton/year of manure, green waste, energy crops, sewage, and organic household waste and assumes all the organic matter to be constant figures, except for the manure and sewage [2]. The ferry requires 2.5 million m3 of methane per year to ensure continuous transportation to and from the island. To fuel other transportation within the island, an additional 1 million m3 methane is required, providing a total desired biogas plant capacity equal to 3.5 million m3 of methane per year. The typical composition of biogas produced from anaerobic digestion of organic waste, including manure and energy crops ranges between 50-70% methane, 30-50% carbon dioxide and trace amounts of water vapor, hydrogen sulfide, and other minerals. Based on the biogas production potential of the biomass on Samsø, the biogas composition needs to be at least 65% methane (not including net lifecycle energy; i.e. the energy needed for the digester operations, feedstock acquisition and delivery, and biogas upgrading and methane supply infrastructure).

To increase the feasibility of biofuel production on Samsø, the biogas plant needs to achieve higher concentrations of methane to ensure there is enough to fulfill both ferry and other transportation needs. One method is to use co-substrate digestion and pretreatment through wet-explosion techniques with separated manure fibers and catch crops, which was used in the Bornholm digester in Denmark to improve efficiency of biogas production [3]. Mechanical methods of pretreatment require less economical investment and increase methane yields [3]. Converting biogas to liquefied biogas (LBG) requires investment in different upgrading and cleaning technologies to ensure the fuel is high quality and stable for transportation, as well as requires special cryogenic compression and storage techniques [4,5]. Since Samsø does not have a biogas facility or gas processing plant to upgrade from biogas to LBG, these cleaning, upgrading, and cryogenic technologies and cryogenic compression and storage techniques need to be included appropriately to improve the efficiency and economics of final LBG production for use with the ferry and transportation system.

The goals of this study are to evaluate the economics of transitioning Samsø’s ferry and transportation fuel source from LNG to LBG to determine the feasibility of a 25 year payback period for


Samsø. This analysis includes investigation on how to reduce cost and increase methane production associated with the biogas plant to improve the overall feasibility of transitioning to LBG. Feedstock composition, throughput and biogas production, as well as upgrading and cryogenic technologies associated with producing LBG from the plant were areas of focus for the investigation. Results from the techno-economic analysis will facilitate decisions by Samsø to further pursue LBG as a transportation fuel.

2. Methods

2.1 Economic Analysis of LNG and LBG The clients at Samsø have a targeted goal of achieving at payback period of less than 25 years to

receive a 0% interest rate loan to transition the LBG. The net present value cost associated with the current fuel source, LNG, for the ferry was determined using a fixed discount rate of 3% with a 25 year lifetime and included capital cost of the dual-fuel engine ferry and annual cost for LNG. The 3% discount rate was chosen based on a study already done on Samsø. Annual cost associated with purchasing and importing LNG from Netherlands, distribution and bunkering was fixed 14 million DKK, based on figures provided by Soren Hermansen and Michael Kristensen of Samsø Municipality. Seventy-two percent of this annual cost is for the price of LNG, 26% is for distribution, and 2% is for bunkering.

Capital cost for the biogas plant is 43 million DKK, per Samsø Municipality estimation, and 35 million DKK for upgrading and cryogenic technology. Annual cost for the biogas plant and upgrading included transportation of biomass to the plant, biomass processing, profit from selling digestate as fertilizer, overhead (employee salary, insurance, administration), cost associated with collection of biomass and bulking agents, operation and maintenance for upgrading and cryogenics, and savings associated with not shipping waste off Samsø for incineration (Table 7.3.1 and Table 7.3.2 in the Appendix) [2]. Cost factors were derived from the January 2015 biogas plant study for Samsø [2]. Net present value of combined capital cost for the ferry and biogas plant and annual cost was determined using a fixed discount rate of 3% with a 25 year lifetime (Table 7.3.3 in the Appendix).

2.2. Biomass and Biogas Production Biomass and biogas production potential of organic waste and matter on Samsø were analyzed

to identify potential sources of feedstock for the biogas plant, as well as expected biogas production capacity for the biogas plant. Metrics were based on reports completed by project partners with Aalborg University Copenhagen that inventoried usable biomass on Samsø. These values represent biomass that will be readily available for use in the biogas plant on a yearly basis.

2.3 Bioprocessing, Upgrading, and Cryogenic Technologies Upgrading techniques for biogas, including scrubbing technologies and cryogenic liquefaction

were analyzed to determine technologies most appropriate for the Samsø biogas plant. The analysis focused on options appropriate for the scale of Samsø, as well as ease of maintenance and economic investment. Vendors were contacted and literature and case studies were reviewed.

3. Results The economic analysis performed in this study is aimed at determining the net present value

associated with ferry project and the payback period for the total amount that will be invested in this ferry project over its lifetime, which is estimated to be about 360 million DKK,. This estimate includes capital costs of building a biogas plant, upgrading facility, setting up the transportation infrastructure,


cryogenic compression technology, and cost of the ferry. The project lifetime is assumed to be 25 years. A detailed breakdown of the estimated costs is presented in Table 3.1.

Table 3.1: Estimated capital costs associated with biogas transitioning to LBG

Category Capital Cost (Millions DKK) Ferry 210 Biogas Plant 43 Upgrading Facility 35 Transportation 3 Compression Technology 35

The capital cost of the ferry and biogas plant was provided by clients in Samsø. The capital costs

associated with the upgrading facility and transportation were estimated from [6] and [7] respectively. The cost of the compression technology (Galileo Cryobox) was determined after consultation with a sales representative from Galileo Technologies, a company supplying the cryogenic technology for this project. The 34 million DKK not accounted for in Table 3.1 are listed as miscellaneous costs, and more information is needed from the client to break down what they consist of.

Based on the assumptions listed in the methods section using a 360 million DKK capital investment, a 3% discount rate, and a fixed 14 million DKK return per year, the discounted payback period was calculated to be about 49.9 years. This scenario is extremely unfeasible as its resulting payback period is very far off from the intended range. Accordingly, a few economic scenarios were analyzed to determine the sensitivity of the payback period to various factors. These scenarios focused on varying the discount rate and cash flow related to added revenue from selling digestate as fertilizer, selling excess LBG for transportation within Samsø, and potential tax benefits from biogas production. Revenue generated from excess LBG was based on selling 1600 m3 LBG/year at a rate of 120 DKK/mmbtu. Potential tax benefits were calculated at a rate of 40.3 €c/m3 methane (2.8 DKK/ m3 methane). Figure 3.1 shows the discounted payback periods for each scenario, where the baseline scenario does not include any potential revenue generated from coproducts or the cost of the ferry. Change in cash flow revenue for the biogas plant showed improved payback periods for each scenario. Under a 3% discount rate, the payback period ranges from 9 to 31 years for the adjusted cash flow scenarios. Calculations and formulas used to calculate the discounted payback period are included in the Section 7.3 of the Appendix.


Figure 3.1: Resulting discounted payback period for multiple cash flow and tax scenarios for LBG fuel system. Cost of the ferry is not included in the payback periods.

The Net Present Value (NPV) of a LBG-based fuel system for the ferry was compared to the NPV of the present LNG system in Samsø. This analysis was done to draw a relative comparison between the economics of the LBG ferry project and the present LNG system. Currently, Samsø is using LNG to operate the ferry and this LNG is imported by Samsø at a price of nearly 10 million DKK per year. In addition to the fuel cost, bunkering and distribution costs increase the total spending by Samsø municipality to approximately 14 million DKK a year without any revenue streams to offset the cost. The results from the economic analysis are listed in Table 3.3 and the detailed step by step calculation of the NPV for both projects are shown in the Appendix 7.3.

Table 3.2: Net present value comparison for present LNG system and proposed LBG system for transportation fuel, including capital cost of ferry. NPV does include potential revenue generated from fertilizer production for the LBG system.

Scenario Net Present Value (Millions DKK)

Present LNG System 444

Biogas-LBG System 474

0

5

10

15

20

25

30

35

40

45

50

Baseline Sell Digestate Tax Revenue Sell ExcessLBG

Sell ExcessLBG,

Digestate +Tax Rev.

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Scenarios

Discounted Payback Period for Cash Flow and Tax Scenarios

3% Discount Rate

6% Discount Rate


4. Discussion and Conclusions

4.1 Bioprocessing, Upgrading, and Cryogenic Technologies The focus of this section is to summarize alternative technological pathways that best achieve

Samsø’s biomethane fuel requirements as well as contribute to a reasonable NPV and PBP through high-value-added byproducts from biogas upgrading. This report recommends the following pathway and its associated technologies necessary to achieve optimal production of LBG. In depth analysis of each processing step is provided in Appendix 7.2.

Pretreatment and size reduction of Samsø’s available biomass is necessary to increase the surface area and accessibility of the substrate during anaerobic digestion. Xergi, a Denmark company specialized in implementation of biogas plants, has developed a pretreatment technology called the X-chopper® [8]. It is suggested that Samso use this technology to break down feedstock to achieve a higher concentration of methane per m3 of raw biogas. Purification of biogas goes beyond the removal of carbon dioxide. As previously described, raw biogas contains several contaminants, including water (H2O), hydrogen sulfide (H2S) , nitrogen (N2), oxygen (O2), ammonia (NH3), siloxanes and particles, which must be separated to prevent corrosion and mechanical wear of the upgrading equipment. Although, this study does not suggest specific technology to achieve these requirements, it is recommended that iron oxide be used for the removal of H2S, resulting in the production of solid sulfur (S), which has commercial value and application [9].

Further, the purpose of upgrading is to increase the concentration of methane; i.e. the energy density of the gas. In industrial practice there are several methods for CO2 separation, each having their own advantages and disadvantages. Conventional upgrading technologies include CO2 separation by water scrubbing, pressure swing absorption, chemical scrubbing, physical scrubbing, and membrane separation, while unconventional upgrading processes consist of cryogenic separation of biogas components and hydrogenation/methanation of CO2 to synthetic natural gas (See Appendix, Table 7.2.1). Our client Soren Hermansen had expressed interest in chemical scrubbing, which achieves the highest purity with regard to biomethane concentration (90-99%) with minimal methane losses (<0.1%) when compared against the other conventional techniques. However, this process requires high temperatures and energy demands to regenerate the solvent and this technique fails to achieve adequate recovery of byproducts [10]. Therefore, this report strongly recommends both/either cryogenic separation of CO2, CH4, and N2 by exploiting their different condensation temperature and/or production of synthetic methane (syngas) by methanation: catalytic reaction between hydrogen (H2) and CO2. These techniques are promising because cryogenics can generate liquid CO2, a high-value byproduct, while methanation can boost the concentration of biomethane per unit volume. Syngas production by methanation is exothermic, thereby generating a lot of process heat, which can be recovered at 60% and used for district heating. By capturing process heat from this reaction, the total energy efficiency of the upgrading process can achieve 92% (See Appendix, Figure 7.2.1) [9] Methanation technology is currently commercially available with future potential for cheap and efficient hydrogen supply by companies such as SOEC from Topsøe, Denmark [9].

This thesis for the Samso Island municipality reports several potential solutions for cryogenic liquefaction of purified biomethane to LBG for maritime services. Various technologies were evaluated to determine their suitability in order to meet the technical and economic needs of Samso. The following technologies were researched and compared against one another: Prometheus-Energy, Scandinavian GtS, Acrion Technologies/Terracastus Technologies, Cryostar, Sterling Cryogenics, Dresser-Rand, and Galileo/Verdek LLC. All of the cryogenic technologies examined are capable of isolating CO2, CH4, and N2. After thorough examination –based on criteria including accessibility to datasheets and information regarding the company and their technology; the capital investment and operational expenditures; the type of reference projects and their similarity to the conditions on Samso; modularity


of the unit[s]; versatility (i.e. integrated upgrading system, including separation and recovery of byproducts); size of the equipment/module; output of LBG (gallons/day); ease of commissioning; and mobility –the Cryobox of Galileo Technologies/Verdek LLC is recommended for the Samso municipality ferry service [11]. Galileo’s Cryobox is strongly suggested because it offers a modular cryogenic solution that is capable of upgrading through separation and recovery CO2 and N2. Also, the system can generate CNG, allowing for simultaneous availability of adequate fuel for urban vehicles. The Cryobox is the only self-contained, scalable system currently on the market that achieves these multiple functions all in one integrated system that does not require additional units for operation. In addition, Galileo recently made Buquebus in Argentina the first maritime enterprise to supply its own LNG [12]. The Cryobox is a simple ‘Plug and Play’ technology that is modular, lightweight, transportable, and easy to install, operate and maintain (See Appendix, Figure 7.2.2). One module can produce as much as 9,000 gallons of LBG/day, which is within Samsø’s ferry requirements of roughly 3,000 gallons/day. For about 35 million DKK, including treatment and upgrading technology and commissioning, Samso can become its own LBG supplier.

4.2 Biomass and Biogas Production Based on the results from the previously conducted biomass study on Samsø, all organic matter

available on the island would need to be utilized to produce enough biogas to sustain fuel supply for the ferry and transportation within Samsø. Over half of the methane production is attributed to digestion of energy crops (Table 7.1.1 in Appendix). The projected methane yields for the Samsø’s biomass does not include net lifecycle energy; i.e. the energy needed for the digester operations, feedstock acquisition and delivery, and biogas upgrading and methane supply infrastructure. This means there will not likely be enough methane production to supply the ferry and estimated 1 million m3 methane for transportation within Samsø. Aside from methane production, utilizing all of Samsø’s potential biomass sources may not be realistically feasible since collection will be required increased coordination for waste collection from multiple locations. Also, some of the waste may be more difficult to consistently collect. For instance, residents may prefer to keep their household organic waste to use for home composting. Potential issues and solutions for organic waste collection, including transportation coordination and incentives for farmers and residents needs to be further investigated to ensure a steady supply for the biogas plant.

4.3 Economic Analysis Analyzing the baseline scenario of the LBG fuel system for the biogas plant, which does not

include revenue generated from coproducts or tax benefits, the payback period exceeds 25 years. However, a couple of different scenarios are considered to understand the sensitivity of the payback period on the following variables: 1) Capital Cost and 2) Cash Flow/Year. In order to bring the payback period closer to less than 25 years, either the capital investment has to be reduced significantly or the net positive cash flow per year has to be increased. From a cash flow perspective, tax benefits provided the most significant reduction in payback period, at 3% discount rate it is 11 years. However, revenue generated from selling digestate alone, reduced the payback period to 31 years, but still exceeded the goal of 25 years. Selling excess LBG for transportation within Samsø also decreased the payback period to 19 years. Thus, efforts should be focused on reducing the capital costs in combination with increasing the net cash flow per year.

The NPV analysis in Table 3.2 shows that from a strictly economic perspective, the current LNG system in Samsø is economically more feasible than transitioning to LBG produced on the island if coproducts are not sold or the project does not receive tax benefits. Needless to say, this study does not take into consideration the visibility and social aspects of such a transition. The social and environmental


outcomes of this transition may also be sufficient to justify the investment in this project. A separate study regarding the social and environmental outcomes of this transition needs to be performed in order to flesh out these issues.

5. Recommendations The economic viability of this project is partially contingent on the amount of biomethane that

can be obtained from the overall bioprocess. Beyond pretreatment of the biomass, the use of hydrogenation/methanation of CO2 to synthetic methane would increase the overall methane concentration per unit volume of biogas. This also allows for the reduction in the use of feedstock such as deep litter, which is more difficult to process and yields low amounts biomethane per unit weight of biomass. As previously mentioned, methanation is an exothermic process. The heat produced from this reaction can be recovered and directed toward district heating, which might reduce the amount of biomass needed for CHP purposes [6]. In addition, one opportunity to increase the feasibility of this project by adding to the annual return on investment is to sell liquid CO2 obtained from cryogenic liquefaction.


6. References 1. PlanEnergi. (2014). Biomass resources on Samso for biogas production. EUDP Project: Biogas for

transport. Work Package 1: Feasibility study—biogas production. 2. PlanEnergi. (2015). Biogas plant on Samso. EUDP Project: Biogas for transportation. Work

Package 1: Design and pricing of biogas plants. 3. Molinuevo-Salces, B., Larsen, S. U., Biswas, R., Ahring, B. K., & Uellendahl, H. (2013). Key factors for

achieving profitable biogas production from agricultural waste and sustainable biomass. In World Congress on Anaerobic Digestion.

4. Allegue LB, Hinge J (2012) Overview of biogas technologies for production of liquid transport fuels. Danish Technological Institute.

5. Bauer F, Persson T, Hulteberg C, Tamm D (2013) Biogas upgrading–technology overview, comparison and perspectives for the future. Biofuels, Bioproducts and Biorefining 7: 499-511

6. Dirkse, E.H.M. Biogas Upgrading Using the DMT TS-PWS® Technology.Rep. DMT Environmental Technology, Web. 20 Aug. 2015. <http://www.dirkse-milieutechniek.com/dmt/do/download/_/true/203088/BiogasupgradingusingDMTTS-PWS1.pdf>.

7. Bundgaard, Sirid, and Anders Kofoed-Wiuff. Experiences with Biogas in Denmark. Rep. DTU Department of Management Engineering, Web. Aug. 2015. <http://orbit.dtu.dk/files/97911958/Experiences_with_biogas_in_Denmark.pdf>.

8. Xergi A/S. Hermesvej 1, DK-9539 Storving, Denmark. 9. Johansson, N. (2008) Production of liquid biogas, LBG, with cryogenic and conventional upgrading

technology: description of systems and evaluations of energy balances. Department of Technology and Society. Lunds University. Master’s Thesis.

10. Niesner, J., Jecha, D., Stehlik, P. (2013) Biogas upgrading technologies: state of the art review in European Region. Chemical Engineering Transactions, 35, 517-522.

11. Galileo Technologies. Av. General Paz Provincia 265. Buenos Aires, Argentina. 12. Case Study. (2014). Galileo brings on demand LNG to the maritime industry. Buquebus LNG facility,

Argentina. 13. Evald, A., Hu, Guilin, Hansen, M.T. (2013) Technology data for advanced bioenergy fuels. Danish

Energy Agency: Department of Biomass and Waste

http://www.dirkse-milieutechniek.com/dmt/do/download/_/true/203088/BiogasupgradingusingDMTTS-PWS1.pdf

http://www.dirkse-milieutechniek.com/dmt/do/download/_/true/203088/BiogasupgradingusingDMTTS-PWS1.pdf

http://orbit.dtu.dk/files/97911958/Experiences_with_biogas_in_Denmark.pdf


7. Appendix

7.1 Biomass and Biogas Production

Table 7.1.1: Biogas production potential of biomass on Samso, including agricultural and household organic waste [1].

Biomass Type Total Resource (tons/year)

Biogas Potential Production (x1000 m3/year)

Cattle Manure 10000 234

Pig Manure 33000 581

Sewage 35000 319

Plowed straw 3000 207

Profit Straw 700 217

Catch Crops 2000 236

Meadow Grass 2000 226

Energy Crops 17500 2748

Vegetable Waste 1400 115

Gardening Waste 3245 276

Household Organic Waste 580 108

Total 108425 5267

7.2 Bioprocessing, Upgrading, and Cryogenic Technologies Biomass pretreatment

Pretreatment and size reduction of biomass is necessary to increase the surface area and accessibility of the substrate during anaerobic digestion. Further, pretreatment increases the potential for methane-producing bacteria (methanogens) to consume the biomass, thus giving a higher gas yield. Xergi, a Denmark company specialized in implementation of biogas plants, has developed a pretreatment technology called the X-chopper®, which can be used to break down materials like turnips, straw, and deep litter (combination of straw and sawdust material used for animal bedding).

Cleaning of biogas

Aside from removal of carbon dioxide to produce biomethane, raw biogas also contains water, hydrogen sulfide, nitrogen, oxygen, ammonia, siloxanes and particles. The concentrations of these impurities are dependent on the feedstock from which the gas was produced [2]. Removal of these components is beyond the scope of this study; however, to prevent corrosion and mechanical wear of the upgrading equipment where carbon dioxide is separated from the biogas, desulphurization and separation of other minor impurities is strongly recommended to clean the raw gas before further use.

Upgrading of biogas

The purpose of upgrading is to increase the energy density of the gas since the concentration of methane is intensified. In industrial practice there are several methods for CO2 separation, each having their own advantages and disadvantages, yet the choice of the economically optimal technology is strongly dependent on the quality and quantity of the raw biogas to be upgraded and the final utilization


of the gas. [3]. Conventional upgrading technologies include CO2 separation by chemical scrubbing, while unconventional upgrading processes consist of cryogenic technology and hydrogenation/methanation of CO2 to synthetic natural gas. Chemical scrubbing, cryogenic technology, and hydrogenation upgrading techniques will be presented and discussed in this text.

Conventional techniques associated with small-scale liquefaction

The most conventional technologies for CO2 separation in the European region at present are: (1) water scrubbing, (2) pressure swing absorption, (3) chemical scrubbing, (4) physical scrubbing, and (5) membrane separation [3] (Table 7.2.1). Samsø municipality expressed strong interest in using chemical scrubbing. This report will outline the advantages of using chemical absorption to separate carbon dioxide, as well as recommend other commercially available upgrading technologies.

Table 7.2.1 Conventional upgrading technologies (Source: Biomethane Regions, 2013)

The principal behind the absorption technique is that carbon dioxide is more soluble than methane. In an upgrading plant using chemical absorption, the raw biogas meets a counter flow of liquid in a column where a chemical reaction occurs between CO2 and the solvent. Chemical scrubbing is strongly selective for CO2, thereby resulting in high methane recovery and very low methane slip [4]. The solvents used in chemical scrubbing are monoethanolamine (MEA), diethanolamine (DEA) or diglycolamine (DEA). CO2 has a higher affinity for amine solvents in comparison to water per unit volume, which also means a lower operating pressure.


From a technical lens, chemical scrubbing is effective at removing CO2 from raw biogas; however, regeneration of the solvent requires high temperatures and energy demand. In addition, hydrogen sulfide can be absorbed in chemical scrubbing as well, however during recovery of the solvent requires greater heating demands. Therefore, desulphurization is recommended prior to chemical scrubbing.

This technique might be ideal for Samsø due to the proximity and connectivity of the biogas facility to excess thermal energy and district heating. Further, a key technological feature of chemical scrubbing is the necessity for high-energy solvent regeneration and high operational costs [4]. In addition, this technology is preferably used for medium or large-scale plants – Samsø being a small-scale operation. Yet, this technique achieves the highest purity of biomethane (90-99%) [5, 6] and minimal methane losses (<0.1 %) [4, 5, 6, 7].

Cryogenic separation

Another technique for preparing biomethane from biogas is the use of cryogenic technologies and exploitation of different condensation temperatures of the compounds that comprise raw biogas.

Three suppliers of cryogenic technology have been identified and their technical solutions are presented [8]. Scandinavian GtS uses their own technology to separate contaminants and CO2 from the gas stream while Prometheus-Energy uses commercial technology to freeze out CO2. Acrion Technologies/Terracastus Technologies use a distillation column to purify the raw gas and CO2 is then separated with membranes and pressure swing adsorption. Table 7.2.2 contains details regarding CH4 and CO2 content, recovery, loss, and purity in LBG for the three cryogenic upgrading technologies presented [8].

Table 7.2.2: Identified suppliers of cryogenic technologies (Source: Johansson, 2008)

The technology is simple. Since biogas is upgraded by chilling the gas to around -80 C at atmospheric pressure to obtain liquid CO2 (LCO2) it results in low CH4 losses and generates a valuable byproduct which has many commercial applications [8]. Clean LCO2 is produced in all three processes but only SGtS and Acrion are capable of recovering it at 100% and 30-50%, respectively [8]. The CO2 free biogas is then cooled to below -162 C where methane is liquefied and nitrogen gas can be easily separated due to its lower condensation temperature [8]. All three cryogenic suppliers reported very low CH4 losses since all vented CH4 is collected and treated. In addition, no chemicals are used in any of the three processes, however they handle a number of refrigerant including nitrogen and/or helium. In addition, both SGts and Acrion use iron oxide for the removal of H2S, although SGts uses a regenerative technique that results in the production of solid sulfur (S), while Acrion uses a non-recoverable process. Prometheus-Energy has not reveled which technology they use for desulphurization [8].

Hydrogenation/methanation


CO2 can be used as a precursor for synthetic natural gas (SNG), or synthetic methane, production through a hydrogenation mechanism. As previously discussed, the main components of natural gas are CO2 and CH4 with their respective concentrations contingent on the biogas production pathway and the type of feedstock (Figure 7.2.1).

Figure 7.2.1: Schematic energy balance of SNG production by methanation of biogas (Source: Johansson, 2008).

Hydrogenation/methanation converts CO2 to methane by reacting with hydrogen gas (H2), which generally requires a catalyst. The methanation reaction is exothermic, thereby generating a lot of process heat, which can be recovered at 60% and used for district heating. By capturing process heat from methanation, the total energy efficiency of the upgrading process can achieve 92%. Hydrogen may be produced by a water electrolysis unit, or supplied by other means. Therefore, the methanation plant may require hydrogen supply/storage as well as biogas storage, depending on local conditions [10]. Further, oxygen is produced as a high-value-added byproduct. Methanation technology is currently commercially available with future potential for cheap and efficient hydrogen supply by companies such as SOEC from Topsøe, Denmark.

Liquefaction technology for maritime conditions

This thesis for the Samsø, Denmark municipality reports several potential solutions for cryogenic liquefaction of purified biomethane to LBG for maritime services. Various companies were evaluated to determine if their technology was suitable in order to meet the technical and economic needs of Samsø. The following technologies were researched and compared against one another: Prometheus-Energy, Scandinavian GtS, Acrion Technologies/Terracastus Technologies, Cryostar, Sterling Cryogenics, Dresser-Rand, and Galileo. Basic criteria included accessibility to datasheets and information regarding the company and their technology; capital investment and operational expenditures; the type of reference projects and their similarity to the conditions on Samsø; versatility (i.e. capability to perform upgrading, including separation and recovery of CO2 and N2, without additional components); size of the equipment; output of LBG (gallons/day); ease of commissioning; mobility; and modularity. After careful consideration, Galileo’s Cryobox is recommended for the Samsø municipality ferry service.


Figure 7.2.2 Properties and characteristics of the Galileo Cryobox (Source: Galileo Technologies).


The Cryobox is designed so that communities like Samsø can become their own LBG supplier. Each module can produce as much as 9,000 gallons of LBG/day – Samsø requires roughly 3,000 gallons/day. The Cryobox can also generated CNG, allowing for simultaneous availability of adequate fuel for urban vehicles (Figure 7.2.2).

7.3 Economic Analysis Table 7.3.1: Annual cost associated with biogas plant operations [1]

Item Category Cost Type Cost Unit (per year)

Income or Debt

Multiplier (Tons)

Total Cost

Unit

Biomass Processing

Sell Digestate 25 Kr/t Income 28,000 700,000 Kr/yr.

Processing 4 Kr/t Debt 108,425 455,385 Kr/yr.

Overhead Employees 1,000,000 Kr Debt 1 1,000,000 Kr/yr.

Administration 200,000 Kr Debt 1 200,000 Kr/yr.

Insurance 400,000 Kr Debt 1 400,000 Kr/yr.

Transportation Deep litter 40 Kr/t Debt 3,000 120,000 Kr/yr.

Straw 40 Kr/t Debt 700 28,000 Kr/yr.

Manure 25 Kr/t Debt 78,000 1,950,000 Kr/yr.

Additional biomass, org. waste

25 Kr/t Debt 26,725 668,125 Kr/yr.

Collection Energy Crops 300 Kr/t Debt 17,500 5,250,000 Kr/yr.

Catch crops 300 Kr/t Debt 2,000 600,000 Kr/yr.

Meadow Grass 500 Kr/t Debt 2,000 1,000,000 Kr/yr.

Straw 600 Kr/t Debt 700 420,000 Kr/yr.

Bulking Agents 50,000 Kr Debt 1 50,000 Kr/yr.

Table 7.3.2: Annual cost associated with LBG fuel source production on Samso for ferry and other transportation

Cost Category Cost Unit Income/Debt

Biomass Processing 455,385 Kr/yr. Debt

Sell Digestate 700,000 Kr/yr. Income

Overhead 1,600,000 Kr/yr. Debt

Transportation (Biomass) 2,766,125 Kr/yr. Debt

Collection (Biomass) 7,320,000 Kr/yr. Debt

Divert waste from Incineration

5,225,000 Kr/yr. Income

O+M for Cryobox 350,000 Kr/yr. Debt

Total Yearly Cost 6,566,510 Kr/yr. Debt


Table 7.3.3: Total net present value of LNG fuel structure and LBG fuel structure, including capital cost of ferry.

LNG LBG Units

Discount Rate 3 3 %

Lifetime 25 25 years

Ferry Cost (Capital) 200,000,000 200,000,000 DKK

Biogas Plant Cost (Capital) - 160,000,000

Annual Cost 14,000,000 6,566,510 DKK

Annual Cost (Net Present Value)

243,784,068 114,343,608 DKK

Total Net Present Value 443,784,068 474,343,608 DKK

Table 7.3.4: Example Calculation Spreadsheet for Payback Period Analysis. Assumptions: 30 million Capital Cost, 17 million Cash inflow per year, 3% interest rate

Year Cash Flow (Millions

DKK) Present Value

Discounted Cash (Millions DKK)

Cumulative Discounted Cash (Millions DKK)

0 -300 1 -300 -300 1 17 0.97 16.5 -283.5 2 17 0.94 16.0 -267.5 3 17 0.92 15.6 -251.9 4 17 0.89 15.1 -236.8 5 17 0.86 14.7 -222.1 6 17 0.84 14.2 -207.9 7 17 0.81 13.8 -194.1 8 17 0.79 13.4 -180.7 9 17 0.77 13.0 -167.6

10 17 0.74 12.6 -155.0 11 17 0.72 12.3 -142.7 12 17 0.70 11.9 -130.8 13 17 0.68 11.6 -119.2 14 17 0.66 11.2 -108.0 15 17 0.64 10.9 -97.1 16 17 0.62 10.6 -86.5 17 17 0.61 10.3 -76.2 18 17 0.59 10.0 -66.2 19 17 0.57 9.7 -56.5 20 17 0.55 9.4 -47.1 21 17 0.54 9.1 -37.9 22 17 0.52 8.9 -29.1 23 17 0.51 8.6 -20.5 24 17 0.49 8.4 -12.1 25 17 0.48 8.1 -4.0 26 17 0.46 7.9 3.9


Present Value = 1/(1+ i)^n, where i = interest rate and n= Year

Discounted Cash Flow = Cash Flow for that year * Present value

Cumulative Discounted Cash = Cumulative Discounted Cash for year n - Discounted Cash Flow for year n+1.

Payback Period: A + |B|/C. Where A = Last period with negative Cumulative Discounted Cash Flow, B =

Value of discounted cumulative cash flow at the end of the period A, and C = Discounted Cash Flow during the period after A.

7.4 Literature Cited 1. PlanEnergi. (2015). Biogas plant on Samso. EUDP Project: Biogas for transportation. Work

Package 1: Design and pricing of biogas plants.

2. Petersson, A., Wellinger, A. (2009) IEA. Biogas upgrading technologies – developments and innovations.

3. Biomethane Regions (2013). Introduction to production of biomethane from biogas a guide for England and Wales (UK). European Federation of Agencies and Regions for Energy and the Environment. Intelligent Energy Europe. http://www.fedarene.org/wpcontent/uploads/2013/10/BMR_D.4.2.1.Technical_Brochure_EN.pdf

4. Niesner, J., Jecha, D., Stehlik, P. (2013) Biogas upgrading technologies: state of the art review in European Region. Chemical Engineering Transactions, 35, 517-522.

5. Dirkse E.H.M., 2009, Biogas upgrading using the DMT Carborex® PWS Technology, DMT EnvironmentalTechnology.

6. de Hullu, 2008, Biogas Upgrading: Comparing Different Techniques, Eindhoven University of Technology

7. TUV (Vienna University of Technology), 2012, Biogas to Biomethane Technology Review 8. Johansson, N. (2008) Production of liquid biogas, LBG, with cryogenic and conventional upgrading

technology: description of systems and evaluations of energy balances. Department of Technology and Society. Lunds University. Master’s Thesis.

9. Pettersson, A., Losciale, M. and Liljemark, S. (2007) LCMG – Pilotprojekt for LMG som fordonsbransle iSverige. Report SGC 177. Vattenfall Power Consultant. Svenskt Gastekniskt Center.

10. Evald, A., Hu, Guilin, Hansen, M.T. (2013) Technology data for advanced bioenergy fuels. Danish Energy Agency: Department of Biomass and Waste

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