Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units

Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units Bioenergy systems for the future 8 distributed h2 production from bioalcohols and biomethane in conventional steam reforming units

bioalcohols and biomethane in

conventional steam

reforming units

A Vita, C Italiano, L Pino

Institute for Advanced Energy Technologies (ITAE), “Nicola Giordano,” National ResearchConsilium (CNR), Messina, Italy

Abbreviations

CSD compression, storage, and dispensing

DDGS distillers dried grains and solubles

ICEV internal combustion engine vehicles

LHV lower heating value (kJ/mol)

MMBtu Million British thermal unit

NREL National Renewable Energy Laboratory

O&M operating and maintenance

WWTP wastewater treatment plants

Bioenergy Systems for the Future http://dx.doi.org/10.1016/B978-0-08-101031-0.00008-9

© 2017 Elsevier Ltd All rights reserved.

ButOH,IN number of mol of feed butanol (mol)

CH4,IN number of mol of feed methane (mol)

EtOH,IN number of mol of feed ethanol (mol)

Glycerol,IN number of mol of feed glycerol (mol)

H2,OUT number of mol of produced hydrogen (mol)

LHVFuel fuel lower heating value (kJ/mol)

LHVH 2 hydrogen lower heating value (kJ/mol)

QRecovered heat recovered from the heat exchange systems (kW)

QReformer heat to support the reformer (kW)

2=day (US DRIVE, 2013) This process ses the coproduction of large amounts of carbon dioxide, the main responsible for theso-called “greenhouse effect.” Therefore, renewable energy sources tuned with suit-able technologies for hydrogen production will be necessary during the comingdecade (Balat, 2008) The use of fuels directly derived (without further synthesis stepsthat involve hydrogen) from renewable sources (biomass and waste) can give animportant contribution to meet the current and future energy requirements

cau-In this scenario, biofuels such as biomethane, bioethanol, biobutanol, and glycerolcan be considered very interesting renewable fuels for hydrogen production (Andrewsand Shabani, 2012; Edelmann, 2001) through conventional SR process The biogas(biomethane) can be produced from a variety of organic raw materials from various

sectors, ranging from zootechnical to agro-industrial Renewable ethanol and butanolcan be derived from fermentation of sugar-based, corn-based, and cellulose-basedmaterials Glycerol can be obtained as a by-product in biodiesel production.The sustainable utilization of these biofuels, due the local nature of the related feed-stocks, will play an important role to increase the distributed hydrogen production, themost feasible approach for introducing hydrogen as an energy carrier in the near/midterm (<2020) This approach requires low capital investment, due to the smallhydrogen capacity initially needed, and it does not necessitate infrastructures forhydrogen transport and delivery Small-scale (distributed) facilities would producefrom<100 to 1500kgH2=day with the production site connected to the fueling sta-tions Small-scale natural gas reformers are commercially available and this technol-ogy that represents the state of the art should be capable of meeting also the hydrogenproduction cost targets when fully deployed Instead, the reforming systems for thedistributed H2production from gaseous and liquid biofuels are not completely matureand required research activities especially on reactor design and catalytic materials.Nevertheless, these systems are expected to move into commercial production inthe midterm (2020) (US DRIVE, 2013) Then, the distributed hydrogen produced

in small-scale reformers can be used for the heat treatment of metals, glass making,microelectronics fabrication, power generator cooling, hydrogenation of food oils,and feeding existing and nascent fuel cell systems However, the greatest potentialgrowth will be in using hydrogen as a distributed fuel for the transportation sector

A recent study by Ludwig-B€olkow-Systemtechnik and Hinicio (2015) identifiedthe most promising green hydrogen production routes that may help to meet ambitiousenergy targets Between these, a possible pathway considers the reforming of biofuelsfor the production of distributed renewable H2 to feed fuel cell electric vehicles(FCEVs) with small-scale fuel processor (FP) Recently, the interest in hydrogen pro-duction from biogas for FCEVs is continuously growing The National RenewableEnergy Laboratory (NREL) elaborated a market study called “Renewable hydrogenpotential from biogas in the United States” (Saur and Milbrandt, 2014) The reportdetails the availability of biomethane from wastewater treatment plants (WWTPs),manure, and industrial/commercial sources, as well as landfills, in the context ofdemand from the FCEV market and other users Besides, a recent study in the bio-energy sector has evidenced the advantages of the alternative fuel utilization to reduceclimate change disorder and to mitigate greenhouse gas (GHG) emission in the envi-ronment (Joselin and Unni Krishnan, 2016)

Thus, decentralized hydrogen production plant using small-scale reformers for gas or liquid biofuels (bioalcohols) may become part of the future sustainable energynetwork Currently, there are different types of biofuels produced from biomassresources that can be used for on-site hydrogen production Particularly, bioalcohols(ethanol, glycerol, and butanol) and biomethane are the more interesting biofuels due

bio-to their high lower heating value (LHV) per mass and their availability In addition,bioalcohols are sulfur- and nitrogen-free oxygenates The main characteristics of thesebiofuels, in term of SR and maximum H2yield, LHV, and starting source, are reported

inTable 8.1 SR hydrogen yield has been calculated considering the theoretical mol ofhydrogen produced from the fuel steam reforming (SR) reaction to H and CO, while

Table 8.1 Main properties of biofuels derived from biomass materials for on-site hydrogen production

SRtheoretical

H2yield

LHV(MJ/kg)

Maximum H2yield (y/2+2x2z) Source

H2/kg ethanol

lignocellulosic biomass(fermentation)

the maximum hydrogen yield considers the fuel conversion to H2and CO2by SRcoupled with water-gas shift (WGS) reactions.

8.2 Biomass feedstocks: routes and technologies for biofuels generation

In both developing and industrialized countries, the demand for bioenergy increasedsignificantly in the last decade, with the primary objective to reduce the fossil fuelsdependence and the GHG emissions in view of climate change In this regard, somestudies of the International Energy Agency (IEA) highlighted a global overview ofbiomass use in the industrial and transport sectors Currently, biomass covers

10% of the global energy supply (IEA, 2015), as evidenced inFig 8.1, while the

Oil: 4202 (31%)

Oil: 3351 (22%) Gas: 2901 (21%)

Hydro: 558 (4%) Nuclear: 676 (5%)

share of fossil fuels in the global energy system is still high (82%) It is estimatedthat new policies and technologies finalized to support the utilization of renewablesources, including biomass, can contribute to reducing in the near/midterm this con-sumption to about 60% (Vakkilainen et al., 2013).

The term biomass refers to the biodegradable fraction of products, waste, andresidues from agriculture (including vegetal and animal substances), forestry, andrelated industries and the biodegradable fraction of industrial and municipal waste.The biofuel or biorenewable fuel is assigned to a solid, liquid, or gaseous fuel that

is predominantly derived from biomass Purification, upgrading, and conversiontechnology finalized to the hydrogen production will be described in the followingparagraphs principally for the bioethanol and biomethane production; nevertheless,information on other alternative promising bioalcohols (n-butanol and glycerol),directly produced from biomass or as a by-product of the process that involves bio-mass, will be also reported

In the current bioenergy scenario, bioethanol and biogas (biomethane) are the mostpromising candidates as biofuels for distributed hydrogen production Apart from bio-diesel, bioethanol and biogas are the most abundant bioderived fuels (EurObserv’ERsite web Accessed 19 May 2016) that show good potential for distributed hydrogengeneration Bioethanol and biomethane can be produced anywhere in the world,and their transportation infrastructures already exist and are undergoing expansion

to meet the increasing demand finalized to promote an energy scenario based on alow-carbon economy (Leitner and Lindorfer, 2016; RFA, 2016; REN21, 2015;European Commission, 2011; RFA, 2006) Other minor renewable bioderived liquidoptions to generate H2include biobutanol and glycerol The actual scenario for thesebiofuels is mostly based on the production as a by-product of other well-developedprocesses Glycerol can be derived as by-product from the production of biodiesel(Verma and Sharma, 2016), while biobutanol comes from the fermentation of sugarybiomass (Cai et al., 2014)

8.2.1.1 Bioethanol

Bioethanol is a promising source for hydrogen production since it can be producedrenewably in large quantities from several biomass sources, such as energy plants,waste materials from agro-industries, or forestry residue materials (Authayanun

et al., 2015; He et al., 2015) It is obtained as a metabolic product by fermentation

of sugar with yeasts and classified as first and second bioethanol First bioethanol eration originated from sucrose-containing (e.g., sugar cane, sugar beet, and sweet sor-ghum) and starchy materials (e.g., maize, wheat, rye, and corn), while secondbioethanol generation is produced from low-cost nonedible lignocellulosic biomass(i.e., wood, grass, and straw) This classification, based on the generation technolo-gies, is adopted for all biofuels, where third and fourth generations include algaeand vegetable oil-biodiesel, respectively Bioethanol contains 20 vol% of ethanol withwater as the major component; additional impurities such as diethyl amine, acetic

gen-acid, methanol, and propanol are present with concentrations ranging between fewppm to 1% (Devianto et al., 2011) The Renewable Fuels Association (RFA,

2015), also known as the leading trade association for America’s ethanol industry,determined 25.7 billion gallons total of bioethanol produced in 2015 The UnitedStates and Brazil are the main bioethanol producers, as shown inFig 8.2

Generally, the process of the bioethanol production includes four steps: treatment, hydrolysis, fermentation, and distillation, as synthesized inFig 8.3(Dan

pre-et al., 2015; Hou pre-et al., 2015) The first-generation ethanol plants utilize either sugar

or starch The pretreatment step consists in the grains milling and subsequent starchliquefaction The second step is the hydrolysis or saccharification, which releases glu-cose monomers into the solution Then, fermentation with yeast converts the sugarinto ethanol (c.10% w/v) and carbon dioxide Finally, the fermentation liquid is dis-tilled to separate and purify ethanol and dehydrated to concentrate ethanol (above99.7% w/v) The bottom distillate is further treated to obtain distillers dried grainsand solubles (DDGS) as animal protein sources The second-generation ethanol

Thailand (1%) Canada (2%) China (3%) Rest of the World (3%) Europe (5%)

Brazil (28%) United States (58%)

Fig 8.2 World bioethanol production (RFA analysis of public and private estimates)

Grains or

ligno-cellulose Pretreatment

First or second generation bioethanol

Stillage (to animal feed and solid fuel)

CO2

Distillation-dehydration

Fig 8.3 Process outline for first- and second-generation bioethanol

utilizes different types of lignocellulosic materials as substrates that require being ken down to sugar molecules by using a combination of heat and enzymatic treat-ments In this case, solid fuel (SF) can be obtained as waste material from thebottom distillate (Lennartsson et al., 2014).

bro-Bioethanol has attracted much interest because of its advantages, such as safe dling, easy transport, biodegradable nature, high solubility in water, low cost, lowtoxicity, sulfur-free composition, and environmental friendliness (Carvalho et al.,2016; Devianto et al., 2011) Bioethanol can easily react in the presence of water

han-by SR reaction, thus providing an important route for hydrogen production In vision

of a low-carbon economy, bioethanol SR is raising particular attention, due to itspotential to be “carbon-neutral” on a life-cycle basis Indeed, the bioethanol conver-sion to hydrogen can be considered CO2-neutral since the carbon dioxide produced isconsumed for biomass growth Moreover, the direct feed of dilute ethanol to thereformer appears a very interesting solution, preventing the expensive costs for eth-anol purification/concentration (Palma et al., 2016) Unfortunately, the presence ofseveral impurities (heavier alcohol, organic acids, aldehydes, and esters) may affectboth the hydrogen yield and the catalyst stability

8.2.1.2 Biobutanol

Biobutanol can be produced by fermentation of sugar beet, sugarcane, corn, wheat,lignocellulosic biomass, starch-based waste packing peanuts, and agricultural wastes(Cai et al., 2014; Qureshi et al., 2010) The fermentation process generates acetone,butanol, and ethanol in roughly 6:3:1 ratio, known as “ABE” (Wang and Cao, 2011)

In comparison with methanol,n-butanol shows higher hydrogen content (13.5 wt% vs12.5 wt%) and higher energy density (26.9 MJ/L vs 16.0 MJ/L) Furthermore,n-butanol can be used directly in existing fuel distribution pipelines (Nahar andMadhani, 2010)

8.2.1.3 Glycerol

Glycerol is obtained as a by-product in biodiesel production (Zamzuri et al., 2016).Massive amounts of glycerol are being obtained in the manufacture of fatty acidsand mostly in biodiesel production where glycerol represents around 10 wt% of theplant product It has low commercial value and high toxicity, due to the presence

of several impurities, such as methanol; water; inorganic salts; free fatty acids;unreacted mono-, di-, and triglycerides; and methyl esters (Yurdakul et al., 2016).There are two main options to use biodiesel-derived glycerol: (a) purification to obtainhigh-purity glycerol for use in food, cosmetics, and pharmaceutical industries and(b) upgrading to produce different value-added chemicals and/or energy using differ-ent valorization routes such as gasification, steam reforming, and supercriticalreforming (Remo´n et al., 2016) Due to the low purity and the high cost of refining,the crude glycerol has good potential for hydrogen production via SR (Senseni et al.,

2016) If the biodiesel production will increase significantly in the future, largeamounts of glycerol will be available for hydrogen production

8.2.2 Biomethane: sources, production, purification and

upgrading

Biogas is produced from the anaerobic digestion of organic material, such as manure,sewage sludge, organic fraction of household and industrial waste, and energy crops.All types of biomass can be used as substrates for biogas production as long as theycontain carbohydrates, proteins, fats, cellulose, and hemicelluloses as main compo-nents Only strong lignified organic substances, for example, wood, are not suitabledue to the slow anaerobic decomposition Biogas is a mixture of methane (35%–77%) and carbon dioxide (30%–60%) with small amounts of other gases andby-products, that is, nitrogen (0%–5%), carbon monoxide (<0.6%), hydrogen sulfide(0.005%–2%), oxygen (0%–3%), and ammonia (<1%) Trace amounts of siloxanes(0%–0.02%), halogenated hydrocarbons (<0.65%), and other nonmethane organiccompounds as aromatic hydrocarbons, alkanes, alkenes, etc are also occasionally pre-sent Usually, this mixed gas is saturated with steam and may contain dust particles.The biogas yield and its content of methane depend directly on the organic composi-tion of the feedstock, as different raw materials have different degradation rates Fatsprovide the highest biogas yield but require a long retention time due to their poorbioavailability Carbohydrates and proteins show much faster conversion rates butlower gas yields The biogas composition, related to different types of feedstock, iscollected in a large number of studies (Delsinne, 2010; Rasi, 2009; Petersson,2007; Lampe, 2006; El-Fadel et al., 1997) InTable 8.2, typical biogas compositions

as a function of the main biogas sources are given These are (i) sewage treatmentplants (primary and secondary sludge resulted from aerobic treatment of wastewater),(ii) landfills, (iii) agricultural organic streams (manure and slurries from different ani-mals, energy crops, catch crops, grass, and other by-products), (iv) industrial organicwaste streams (from food processes as milk and cheese manufacture, slaughter houses,and vegetable canning; from beverage industry as by-products from breweries, fruitprocessing, distilleries, coffee, and soft drinks; and from industrial products, for exam-ple, paper and board, sugar plants, rubber, and pharmaceuticals), and (v) municipalsolid waste (organic fraction of household waste)

Actually, most of the biogas is combusted in internal combustion engines (ICE) toproduce electric power and heat Moreover, the methane in biogas can be also utilized

as vehicle fuel or as source to produce hydrogen via reforming processes for long-term application (2020–30) (LBST-Hinicio, 2015) For the upmentioned appli-cation, where it is important to have high energy content in the gas stream, the biogaspurification and upgrading into biomethane are required Several technologies for bio-gas purification and biogas upgrading are commercially available and others are at thepilot or demonstration plant level In those upgrading technologies, in which carbondioxide is separated from the biogas, some of the other unwanted compounds are alsoseparated However, to prevent corrosion and mechanical wear of the upgradingequipment, it can be advantageous to clean the biogas before the upgrading (Lo´pez

medium-et al., 2012) The purification step relates to the main impurities that can be found

in biogas, such as sulfur, halogenated hydrocarbons, organic silicon compound anes), oxygen, nitrogen, ammonia, water, and particulates The principal technologies

Table 8.2 Biogas composition

Components

Municipalwaste

Wastewater

Agricultural animalwaste

Waste from agrofood

for the abatement of sulfur are adsorption on activated carbon, chemical absorption,and biological treatment Siloxanes can be removed by cooling the gas; by adsorption

on activated carbon (spent after use), activated aluminum, or silica gel; or by tion in liquid mixtures of hydrocarbons Siloxanes can also be removed while sepa-rating hydrogen sulfide Oxygen and nitrogen can generally be removed indesulfurization processes or in some of the biogas upgrading processes Ammonia

absorp-is usually separated when the gas absorp-is dried or when it absorp-is upgraded Water can beremoved by cooling, compression, absorption, or adsorption methods Particulatesare separated by mechanical filters Regarding the separation of CO2, the most widelyused technologies for biogas upgrading are pressure swing adsorption (PSA), waterscrubbing, organic physical scrubbing, and chemical scrubbing (Petersson andWellinger, 2009) A comparison between the principal parameters for commonupgrading processes is reported in Table 8.3 (Urban et al., 2008) The choice ofthe most suitable technology depends on specific parameters, such as the availability

of cheap heat and the electricity price It should also be noted that it is often possible toincrease the methane purity and to lower the methane loss but at the expense of ahigher energy consumption

Waterscrubbing

Organicphysicalscrubbing

Chemicalscrubbing

Refers to raw biogas with <500 mg/m 3

of H 2 S For higher concentrations, precleaning is recommended also for the other techniques.

Actually, the use of biomethane as a transport fuel is increasing The largest kets are in Europe, where roughly 10% of the biomethane produced is used in thetransport sector (EurObserv’ER site website Accessed 19 May 2016) As example,

mar-in Sweden, the biogas used for the transportation has reached 88,744 toe, mar-in Germany42,992 toe, and 1462 toe in Finland In addition, Germany and Italy support a stronginfrastructure for natural-gas-based (methane) vehicles with more than 900 natural gasrefueling stations The upmentioned initiatives can be considered preparatory for analternative and more sustainable utilization of the biomethane finalized to the on-sitehydrogen production to feed FCEVs by filling stations based on reforming process

8.3 Biofuels reforming for distributed hydrogen

production

The catalytic SR is a well-developed and highly commercialized process for scale application, through which almost all hydrogen worldwide is produced(Khothari et al., 2008; Sperling and Cannon, 2004) Industrial (chemical and petro-chemical) methane steam reforming (MSR) plants have a size ranging between

large-5000 and 200,000 Nm3/h, which translates into hourly production rates of

450–18,000kgH2=h (US DRIVE, 2013) This production plant may enjoy lower duction cost, but the cost related to the hydrogen production is mostly linked to thedistribution cost (40%–75%) from the large central plant to the various users Itincludes compression, transport, and storage costs

pro-However, the small/medium capacity of hydrogen production plants from biofuelscan allow the development of decentralized infrastructures for on-site hydrogen pro-duction In this scenario, renewable hydrogen may be produced in semicentral facil-ities, located on the edge of urban areas or industrial sites, reducing the cost andinfrastructure needed for hydrogen delivery Small-scale facilities would producefrom <100 to 1500kgH2=day with the production site at the fueling stations(US DRIVE, 2013) Medium-scale (also known as semicentral or city gate) facilitieswould produce from 1500 to 50,000 kgH2=day on the outskirts of cities (US DRIVE,

2013) The small-/medium-scale steam reformers can be considered as downscaledversions of the large-scale SR technology The reforming process simply consists

in transforming hydrocarbons into hydrogen, but important steps as feedstocks fication and hydrogen upgrading must be included in the global system Thus, theoverall process for hydrogen production from biofuels takes place in four main stages(seeFig 8.4): (i) purification of the biofuel, (ii) reforming of the clean biofuel, (iii) COcleanup, and (iv) H2purification

puri-The purification section has been discussed before and depends on the type ofbiofuels In the steam reforming (SR) unit, the clean biofuel reacts with steam inthe presence of a catalyst to produce a synthesis gas composed mostly of H2and

CO, by the following general reaction (Eq.8.1):

CxHyOz+ðx  zÞH2O! xCO + y=2 + x  zð ÞH2 ΔH° > 0
(8.1)

The amount of steam varies depending on the biofuel Indeed, the reforming of ethanol and other bioderived liquid fuels requires higher steam content compared withthe reforming of biomethane (Contreras et al., 2014) The main disadvantage of SRprocess is its endothermicity, which means the need for a significant amount of heatprovided by an external source The process is markedly favored at high temperature,low pressure, and excess steam to limit carbon deposition In the conventional large-scale plant, the steam reforming reaction is carried out over a catalyst contained inparallel vertical tubes placed inside a radiant furnace The heat is usually supplied

bio-by burning part of the fuel feedstock and transferring the liberated heat to the steamreforming reaction Similarly, in a small-/medium-scale system, a part of the biofuel

is burned in a combustor thermally integrated with the reforming reactor Suitableoperating temperatures range between 973 and 1173 K

Then, the carbon monoxide contained in the hydrogen-rich syngas exiting thereformer passes through a WGS reactor that converts the CO into H2 and CO2(Eq 8.2) by using the steam available in the syngas or additional steam added tothe system In practice, based on the CO content in the reformate and on the final uti-lization of the syngas, this cleanup step can include a high-temperature shift (HTS)reactor operating between 473 and 673 K and a low-temperature-shift (LTS) reactoroperating between 400 and 450 K:

CO + H2O$ H2+ CO2 ΔH°

Finally, the dry reformate is cooled to ambient temperature and sent to a purificationunit PSA is the more adequate technology for H2 separation for capacities of

50–1000 Nm3/h (Xia et al., 2016) Two kinds of PSA are recognized: PSA to separate

H2 and/or PSA to separate CO2, followed by a condensation step to remove theremaining H2O Both PSA separation techniques are commercial but energy-intensivetechnologies; they can provide various degrees of H2purity (up to>99%) in depen-dence of the final utilization (Majlan et al., 2009; Ribeiro et al., 2008; Voss, 2005;Warmuzinski and Tanczyk, 1997) Besides, unwanted gases, mainly CO, can be

Compressor

Flue gas

Blower

Heat exchanger

Off gas

PSA HTS

LTS

Heat exchanger

Heat exchanger

H2O tank

removed by using absorbing beds, while the not separated H2residual fraction can berecycled as fuel for heat generation in the reforming step Another promising purifi-cation technology capable to produce high H2purity (>99%) involves the Pd-basedmembrane for H2 separation Unfortunately, this process is considered at momentuneconomic (Adhikari and Fernando, 2006).

Commercial FP units, following the previously described configuration, have beendeveloped by several suppliers; these systems are generally designed for distributed

H2production from natural gas and biogas (Specchia, 2014; Phyrenees Association,

2010) Some of the existing suppliers and the principal characteristics of the FP unitsare reported inTable 8.4(http://www.helbio.com, 2016;http://www.hygear.nl, 2016;

http://www.hyradix.com, 2016;http://www.kakoki.co.jp/english, 2016;http://www.ztekcorporation.com, 2016)

The performance of a reforming system can be evaluated by its overall efficiency

ηH2

, calculated by the ratio between the LHV of the hydrogen produced to the LHV

of the fuel consumed (Real et al., 2016; Kolb, 2008), as follows:

The energy conversion efficiency of large-scale MSR plants is about 75%–80%,although an efficiency of 85% might be achieved by optimization of heat recoveryand utilization and recycling of the off gas coming out from PSA step (Chaubey

et al., 2013)

A more practical performance measure of a reforming system is the overall thermalefficiency (ηth), which includes all the other additional energy provided and recovered(Q) from the system (Northrop et al., 2012):

ηth¼ nH2 LHVH 2

whereQ ¼ QReformerQRecovered;QReformeris the heat needed to support the reformer(including the heat for the steam generation), whileQRecoveredis the heat potentiallyrecovered from the heat exchange systems The US Department of Energy (DOE)adopted a similar definition of efficiency, introducing also the electricity energy deliv-ered to the system (Thomas et al., 2009) Actually, the DOE target related to the

Table 8.4 List of suppliers of SR units for distributed hydrogen production

H2qualityVol (%)

H2capacity(kg/day)

DimensionsaL×W×H (m)

Start-up time cold-warmload variation

n.a.dMitsubishi Kakoki Kaishae

(Japan)

431

3.42.73.37.58.73.3

4 h–n.a30%–100%

ZTEKf(United States) Natural gas 99.99% 36

243

1.81.81.8n.a.d

n.a.dn.a.dHyradixg(United States) Natural gas

Biogas

215

2.35.02.52.36.12.5 2 h 45 min–1 h 30 min30%–100%

a Total mounting space including Balance of Plant (Bop).

b http://www.hygear.nl Accessed 5 July 2016.

c http://www.helbio.com Accessed 5 July 2016.

d n.a ¼ not available.

e http://www.kakoki.co.jp/english Accessed 5 July 2016.

f http://www.ztekcorporation.com Accessed 5 July 2016.

g http://www.hyradix.com Accessed 5 July 2016.

energy efficiency of distributed hydrogen production from natural gas (biomethane) isfixed at 75% and 70%–75% from biomass-derived liquid fuels by 2020 (http://energy.govAccessed 7 July 2016).

On-site hydrogen production is an attractive and versatile way to facilitate the sition to a hydrogen-based economy in the near term The main advantage in the pro-duction of local and near-use hydrogen is the overcoming of the problem related to thelack of dedicated infrastructures In addition, the production of distributed hydrogenthrough biofuel pathway has low-carbon footprint compared to the hydrogen pro-duced from natural gas or other fossil fuels To do this, several technology challenges,such as reducing the cost of the feedstock production/purification, increasing the H2production efficiency, reducing the H2costs, and developing active and durable cata-lyst, need to be overcome The US DOE set numerical targets regarding the hydrogenproduction cost, expressed in$/kg or $/gge (a gallon of gasoline equivalent, gge, isapproximately equal to a kilogram of hydrogen on an energy-content basis) Thesetargets should serve as guidelines in hydrogen production in both research area anddevelopment/demonstration activities (Ruth and Joseck, 2011; Lomax, 2007) Thecost is independent of the technology pathway and takes into consideration a range

tran-of assumptions for FCEVs to be competitive with gasoline internal combustion enginevehicles (ICEVs) In the early market time frame of 2015 to
2020, the hydrogen costtargets have been set up at 7$/kg, untaxed and dispensed at the pump (Joseck andSutherland, 2015) Considering the DOE technical targets for biomass-derived liquidfuel (http://www.energy.govAccessed 7 July 2016), the cost of distributed production

of hydrogen (plant capacity¼1500kgH2=day) from bioethanol reforming could bereduced from 6$/kg (7.7$/kg, dispensed) to 2.3$/kg (4$/kg, dispensed) duringthe time frame of 2015–20 InFig 8.5is a reported comparison between the scenariorelative to 2015 and 2020 considering the breakdown of the costs for distributedhydrogen production by bioethanol reforming

From the analysis of the data in Fig 8.5, the target cost of 4$/kg hydrogendelivered and dispensed could be achieved if the feedstock cost is reduced and theequipment cost and efficiency targets are met

Similar considerations can be done for the distributed hydrogen (plantcapacity¼1500kgH2=day) produced from biomethane obtained by biogas upgrading

In general, because of the wide variety in resource quality and accessibility, there isconsiderable uncertainty and subjectivity in estimating biomethane extraction costsfrom biogas sources Murray et al (2014) estimate this cost including recovery,upgrading, and purification; the production costs of biomethane from WWTPs depend

on the facility size, due to economies of scale, the granularity of unit operations,and the diminishing returns Considering plant with a capacity between 10 and

200 million gallons per day (MGD), the cost of biomethane varies between 1.4and 2.9$/MMBtu Hydrogen production cost from biomethane using MSR is esti-mated equal to 2.94$/kg (4.73$/kg, dispensed) for a reforming small-scale plant

(1500 kgH

2=day) (Milbrandt et al., 2016;http://www.hydrogen.energy.govAccessed

14 July 2016) The production cost decreases by increasing the plant capacity (0.89$/kgfor a plant of 50,000 kgH2=day) InFig 8.6is a reported breakdown of the costs fordistributed hydrogen production by biomethane reforming The feedstock cost (bio-methane) is lower compared with the cost of bioethanol (Fig 8.7, 2015 scenario),while the other cost contributions are similar The cost of hydrogen production from

(a) Feedstock : 5.1 (66%)

(d) O&M: 0.2 (3%)

(c) Capital cost: 0.7 (9%)

(b) CSD: 1.7 (22%) 2015

2020

(a) Feedstock : 1.6 (39%)

(d) O&M: 0.2 (5%)

(c) Capital cost: 0.5 (13%) (b) CSD: 1.7 (43%)

Fig 8.5 Breakdown ((a)¼feedstock cost; (b)¼compression, storage, and dispensing, CSD;(c)¼production unit capital cost; and (d)¼operation and maintenance, O&M, cost) of H2costs

in$/kg for distributed hydrogen production (1500kgH 2=day) from bioethanol reforming (http://www.energy.govAccessed 7 July 2016)

biomethane strongly depends on the chemical composition of biogas, which mainlyaffects the operating and maintenance (O&M) cost, related to purification/upgradingtreatments In general, the O&M cost should be reduced by developing more flexiblesystems In addition, the composition of biogas can vary during the annual production,affecting the performance and the stability of the catalytic reformer.

The reliability of balance of plant (BOP) equipment (pumps, compressors, blowers,sensors, etc.) is often the limiting factor in overall system reliability Another technicalaspect to address regard the physical footprint of the reforming plant As reported in

Table 8.4, suppliers have recently improved the compactness and the capacity ofsmall-scale reformers, but further improvements are needed to reduce costs and toincrease efficiency Also control and safety issues, including on-off cycling, requireimprovement Effective operation control strategies are fundamental to minimize costand emissions, to maximize efficiency, and to enhance safety, but costs still remainhigh due to complex system designs and high-cost sensors In addition, SR and

(a) Feedstock : 2.03 (42%)

(d) O&M: 0.31 (7%)

(c) Capital cost: 0.6 (13%) (b) CSD: 1.79 (38%)

Fig 8.6 Breakdown ((a)¼feedstock cost; (b)¼compression, storage, and dispensing, CSD;(c)¼production unit capital cost; and (d)¼operation and maintenance, O&M, cost) of H2costs

in$/kg for distributed hydrogen production (1500kgH 2=day) from biomethane and natural gasreforming (http://www.hydrogen.energy.govAccessed 14 July 2016)

CO + H2+H2O

WGS unit operations also generate considerable costs, which can be lowered by oping catalysts capable of increasing the activity performances in term of H2yield.

devel-8.4 Novel catalytic formulations for steam reforming process

8.4.1.1 Bioethanol

The bioethanol steam reforming (ESR) reactions are listed in Eqs (8.6), (8.7), inwhich ethanol reacts with steam to form CO and H2(Eq.8.6), producing 4 mol ofhydrogen for 1 mol of ethanol reacted The CO then reacts with steam in the WGSreaction (Eq.8.2) to form CO2and additional H2 The overall reaction of hydrogenproduction by steam reforming of bioethanol (Eq 8.7) is obtained by addingEqs (8.2), (8.6), according to which the maximum yield of hydrogen is 6 mol for

1 mol of ethanol reacted (Banach and Machocki, 2015) This involves the total

dif-is complex and dif-is comprdif-ised by several secondary reactions (Eqs.(8.8)–(8.20):

Methane steam reforming: CH4+ H2O! CO + 3H2 (8.9)Acetic acid formation: CH3CH2OH + H2O! CH3COOH + 2H2 (8.10)Decomposition to methane: CH3CH2OH! CH4+ CO + H2 (8.11)Dehydration to ethylene: CH3CH2OH! CH2CH2+ H2O (8.12)Ethylene steam reforming: CH2CH2+ H2O! 2CO + 4H2 (8.13)Dehydrogenation to acetaldehyde: CH3CH2OH! CH3CHO + H2 (8.14)Acetaldehyde decomposition: CH3CHO! CH4+ CO (8.15)Condensation to acetone: 2CH CH OH! CH COCH + CO + 3H (8.16)

The final hydrogen yield/efficiency depends on the operating conditions, mostlybecause of the equilibrium of WGS and methanation reactions (Eqs (8.2), (8.8)).Moreover, it is strictly connected to the intensity of the secondary reactions(Eqs 8.8–8.20), which can produce by-products (e.g., carbon monoxide, methane,acetaldehyde, acetone, and ethylene), thus reducing H2 yield and causing catalystdeactivation by coke deposition (Montero et al., 2015) Carbon formation is affected

by the Boudouard reaction (Eq.8.17), methane cracking (Eq.8.18), ethylene position (Eq.8.19), and carbon gasification (Eq.8.20):

The equilibrium composition, calculated at fixed steam/EtOH molar ratio equal toone, varying temperature (570–1170 K) and pressure (1–10 bar), is reported in

Fig 8.8 The calculation has been done by using a commercial steady-state simulationpackage named Aspen Plus, based on the minimization of Gibbs free energy of each ofthe existing species Values are expressed as molar fraction on dry basis for a system

composed of CH3CH2OH, H2O, H2, CO, CO2, CH4, and by-products Ethanol wasfound absent from products distribution in every case Hydrogen concentrationincreases by increasing temperature Analogously, CO concentration increases, while

CO2and CH4concentrations decrease with temperature Moreover, other by-products(e.g., ethylene, acetaldehyde, and acetone) were found absent from product distribu-tion (maximum molar fraction 106) It can be noticed that H2concentration decreases

by increasing pressure mainly due to lower methane conversion

The hydrogen yield was calculated based on the theoretical stoichiometric mum of ethanol conversion (SR and WGS) to H2and CO2(H2/EtOH¼6 mol/mol),toward the equation H2,OUT/(6EtOH,IN).Fig 8.9shows the H2yield calculated vary-ing temperature (570–1170 K) and steam-to-carbon molar ratio (steam/EtOH from 1

maxi-to 5) H2yield increases noticeably with temperature until a maximum is reached (inthe 870–1170 K range, depending on the steam/EtOH molar ratio) by promotingeffectively both SR and WGS reactions The maximum H2yield is reached at lowertemperature as the steam/EtOH ratio is increased

There are numerous papers in literature regarding catalysts for ESR, some of whichare reported inTable 8.5 Among the studied active phases, both noble metal-basedcatalysts (e.g., Ru, Rh, Pd, Pt, and Ir) and nonnoble metal-based catalysts (Ni and Co)are found to be promising candidates for ESR reactions Moreover, the behavior ofactive phases over different supports (e.g., Al2O3, SiO2, TiO2, CeO2, and Nb2O5) hasbeen investigated As reported by Contreras et al (2014), catalysts with the bestperformance are characterized by (i) the best active metals and (ii) the best support withspecial surface characteristics Moreover, the preparation method and the operative con-ditions can help to increase hydrogen selectivity, reducing the formation of cokeand by-products Among all noble metals, Rh catalysts are more active and selective

to H2production, favoring the CdC bond cleavage Ruthenium shows performancesimilar to rhodium but rapidly deactivates by coke deposition (Coronel et al., 2014)

570 0 20