University of Groningen Techno-Economic Modelling of Biogas Infrastructures Hengeveld, Evert Jan

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University of Groningen

Techno-Economic Modelling of Biogas Infrastructures

Hengeveld, Evert Jan

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Publication date: 2019

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Hengeveld, E. J. (2019). Techno-Economic Modelling of Biogas Infrastructures: Biogas transport in pipelines. Rijksuniversiteit Groningen.

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SUMMARY

Biogas is produced from biomass by means of anaerobic digestion (AD). Biogas consists mainly of methane and carbon dioxide. The volume percentages for these two parts are in a range of 50% -70% for methane and 30% -50% for carbon dioxide. The composition and the volume of biogas depends on the type of biomass, the type of digester used in the process and on process parameters such as retention time and temperature. Biogas, upgraded to so-called ‘green gas’ or ‘biomethane’, can replace natural gas. Alternatively, biogas can be used to produce electrical power and heat in a combined heat power (CHP) installation.

The quantity of produced biogas is modest as compared to other energy sources. In 2014 global biogas production was only around 1% of natural gas production in that same year. Half of all biogas produced in 2016 was produced in Europe. Large differences exist between countries with respect to types of substrates, end-users and volumes of biogas produced. Feed-in tariffs or feed-in premiums are in place in many European countries to support electricity generation from biogas. Several scenario studies covering the next decades up to 2050 have been made. Although they do not show estimates for the volumes of biogas to be produced, biogas is expected to play its role in specific applications, e.g. transportation fuel, replacement of natural gas, or to provide flexibility in the supply of electricity. Biogas research aims at increasing biogas production along several routes, covering topics such as microbiology of the digestion process, pre-treatment of substrates, digester technology, biogas supply chain analysis, integrate biogas use in the energy system and the use of digestate.

Biogas production is currently often small scale, and thus decentralized. Decentralized production of biogas can be combined with large scale, centralized use of biogas. Biogas from several production units can be collected at a location where either the biogas is upgraded to green gas, or used in energy production in a CHP. A larger scale induces, in general, lower costs per unit and higher energy efficiency. On the other hand, collection of biogas to a large centralized plant adds to the overall costs and reduces energy efficiency. Transport of biogas can be done using dedicated pipelines. Moreover, transport of biogas decouples the location of production of biogas from the location of biogas use e.g. it facilitates biogas production at an agricultural site and use at a town, village or industrial area where power and heat may be needed.

This thesis aims at quantifying the impact of biogas grids on the biogas producer-user chain. In a techno-economic evaluation biogas transport by means of dedicated pipelines is modelled to calculate cost and energy use; multiple digesters produce biogas that is transported to a central location, a hub. At the hub end-use options are upgrading biogas to green gas and injection of this green gas, or biogas use in a CHP. Biogas producer-user chains are evaluated at farm scale and at regional scale. Incorporation of a biogas grid creates flexibility in the design of a biogas value chain.

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Within this context this leads to the main research question:

To what extent can a biogas infrastructure using pipelines support a viable biogas-production-user chain?

Four sub questions were formulated that are separately discussed:

(1) When does decentralized production of biogas and centralized upgrading and injection into the

natural gas grid make sense?

A model was developed to describe a green gas production chain that consists of several digesters connected by a biogas grid to an upgrading and injection facility. The model calculates costs and energy use for 1 m3 _{of green gas. Calculation of cost price and energy consumption}

were done for a chain with decentralized production of biogas, i.e. a configuration with several digesters, and a centralized green gas production chain using a single digester.

The model showed that no energy advantage per produced m3_{green gas can be created}

using a biogas grid and decentralized digesters instead of one large-scale digester. Production costs using a centralized digester are lower, in the range of 5 €ct m-3_{to 13 €ct m}-3_{, than in a}

configuration of decentralized digesters. The model calculations also showed the financial benefit for an operator of a small-scale digester wishing to produce green gas in the cooperation with nearby other producers.

Subsidies and legislation based on environmental arguments like reduction of biomass transport distances, could encourage the use of decentralized digesters in a biogas grid. (2) What costs and energy use are associated with biogas transport by dedicated pipelines at regional

level?

A model was developed to describe a regional biogas grid that is used to collect biogas from several digesters and deliver it to a central point. The model minimizes transport costs per volumetric unit of biogas in a region. Results are presented for different digester scales, different sizes of the biomass source area and two types of grid out: a star out and a fishbone lay-out. A fishbone lay-out presumes cooperation between biogas producers in biogas transport, while in a star lay-out producers do not cooperate in biogas transport.

The model shows that transport costs in a fishbone lay-out at a digester scale of 100 m3 _h-1

are less than 10 €ct m-3_{while for the star lay-out costs can go up to 45 €ct m}-3_{. For 1800 m}3 _h-1

digesters, these values are 4.0 €ct m-3_{and 6.1 €ct m}-3_{, respectively. The results indicate that}

cooperation between biogas producers in collecting biogas by means of a fishbone lay-out reduces the biogas transport costs relative to using their own pipeline in a star lay-out. Merging smaller digesters into a smaller number of larger ones reduces the costs of biogas transport for the same biomass source area.

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(3) How much and at what costs can biogas be stored in a regional biogas grid?

A dedicated grid, used for biogas transport, can serve as a form of biogas storage as well. So a model was developed to evaluate line-pack storage in a transport grid for different digester scales, number of digesters, region size and grid type. Line-pack storage does not require additional investments but variable costs increase because of extra compression costs. Line-pack storage costs are similar in both lay-outs. They are estimated to be between 0.3 €ct m-3 _h-1

and 1.5 €ct m-3 _h-1_{. In a fishbone lay-out, which is preferred for biogas transport, the maximum}

line-pack storage volume is small in both a small sized region and in a large region, as a result of pipeline volume and a pressure restriction. A comparison of storage costs shows that line-pack can compete on costs with pressureless storage, but pressurized pipes are preferred for seasonal storage. A method to describe enlargement of line-pack storage by increased investment in pipelines depending on maximum transport pressure was presented. Such enlargement by applying larger pipe diameters could be financially sensible.

(4) What are potential advantages in heat and power production when biogas is collected from

several digesters using dedicated pipelines?

In the case study “West Flanders” costs of electricity and heat production were calculated for a dedicated biogas grid using pipelines implemented to centralize energy production in a region. A large scale centralized combined heat and power (CHP) engine can produce additional electrical power at a hub, i.e. central collection point, and has lower specific costs compared to decentralized CHPs at digester sites. Biogas transport costs, partly balanced by a scale advantage in CHP costs, are attributed to the additional electrical energy (80%) and heat (20%) produced. If the hub is at a digester site, costs of additional electricity can be as low as 4.0 €ct kWh_e-1_and

are in many cases below 12 €ct kWh_e-1_{, i.e. in the same order of magnitude or lower than costs of}

electricity from biogas produced using separate CHPs at the different digester sites; costs of heat at the hub show to be lower than 1 €ct kWh_th-1 _{assuming an effective heat use of 50%. In case a}

hub is situated at a location with high potential heat demand, i.e. a heat sink, transport of biogas from one digester only to a central located hub can provide 3.4 MW_th of heat at 1.95 €ct kWh_th-1_.

For such a centrally located hub additional electrical energy costs show to be slightly higher, but with three or more digesters these costs are lower than 20 €ct kWh_e-1_{and heat costs are around}

0.5 €ct kWh_th-1_{. With a centralized hub more renewable energy is produced, i.e. a more efficient}

use of biomass feedstock. It is concluded that costs for additional electricity and heat can be at a competing level and scale advantages in a CHP can be a driver to collect biogas at a hub using a biogas grid. The reference value for renewable heat is 2 €ct kWh_th-1_.

In response to the main research question it can be stated that model results in the four studies show that a biogas pipeline infrastructure may, under preconditions, contribute to viable biogas supply chains. The quantification of transport costs and line-pack storage costs makes it possible to estimate the impact of implementation of a biogas grid on final energy costs at the end-user. Line-pack storage adds to flexibility in the energy system. The collection of biogas at a hub induces scale advantages, with regard to investment and energy efficiency.

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Environmentally, decentralized biogas production reduces biomass transport distances and transport movements per digester.

As a result of a discussion on sustainability of utilization of biomass and introduction of a bio-based economy the use of energy crops for biogas production will be diminished. In further research other biogas-producer-user chains could be analysed, whereby biogas production and use are spatially separated and when scale advantages are expected. Research could also aim at extending the model by introducing flexible electricity or heat production; storage of biogas, including a contribution of line-pack storage in the biogas grid can support such flexibility. For the energy systems that include a biogas grid, business models have to be developed.

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