Sustainability of an energy conversion system in Canada involving large-scale integrated hydrogen production using solid fuels

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International Journal of Energy and Environment (IJEE), Volume 2, Issue 1, 2011, pp.1-38
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2011 International Energy & Environment Foundation. All rights reserved.

5
membrane separation of CO
2
. There are two options for using chemical looping combustion during the
reduction and oxidation processes to produce two streams (hydrogen and CO
2
). The first option is after
gasification by using syngas to reduce the metal oxides and the second is by using solid fuels directly
with metal oxides [42-44].

2.3 Anaerobic digestion
Anaerobic digestion is a biological process in which organic wastes are converted in the absence of air to
biogas, i.e. a mixture of methane (55-75 vol. %) and carbon dioxide (25-45 vol. %) as well as small
amounts of hydrogen sulphide (H
2
S) and ammonia (NH
3
). During anaerobic digestion, typically 30-60%
of the solid input is converted to biogas [45]. The by-products consist of an undigested residue and
various water-soluble substances. Depending on the digestion system (wet or dry), the average residence
time is between ten days and four weeks. The use of biomass and organic waste streams via anaerobic
digestion has the potential to play a key role in fostering energy recovery from biodegradable waste in a
sustainable manner [46]. With current developments in reformer technologies, hydrogen can be produced
from methane derived from anaerobic digestion of organic waste material, much of which is currently
land filled [47].

2.4 Advanced pressurized fluidized bed combustion
Pressurized fluidized bed combustion (PFBC) of solid fuels to produce electricity [48] uses a
combination of Brayton and Rankine power cycles. In the proposed system, electricity generated by
PFBC is used for several utilities within the system and the remainder is used to split water into
hydrogen and oxygen in an high temperature electrolyser [48,49]. The heat for the electrolyser is derived
from the PFBC. PFBC can also be coupled with a gasification process by having only part of the solid
fuel gasified (partial gasification) for hydrogen production and combusting the char remaining from the
partial gasification step in the PFBC unit to produce steam for electricity generation [14]. This is one of
the reasons for opting to use PFBC in the proposed system, which is in addition to it being one of the
most efficient combustion processes for solid fuels, along with ultra-super critical pulverized coal
combustion [2,14,50].

2.5 Secondary conversion processes
After a syngas is produced from gasification, it is cooled, cleaned of solids and sulphur (Figure 1)
through various processes [51] and sent to the water-gas shift reaction [24], where the CO in the syngas
is converted to H
2
and CO
2
using steam. Then, the hydrogen is separated from CO
2
using membrane
reactors [50] and sent for purification using the pressure swing adsorption (PSA) process. The purified
hydrogen is stored. An alternative prospective approach is to use chemical looping combustion to reduce
CO and produce separate streams of hydrogen and CO
2
. The hydrogen from direct chemical looping is
also sent to the central hydrogen storage after cooling to remove water.
The methane and CO
2
produced using anaerobic digestion passes through an auto-thermal reformer
(ATR), which has been reported to yield a product with fewer trace impurities than other coal-based
hydrogen production processes, mainly due to the higher operating temperature generated by the
oxidation step [51]. The produced hydrogen, which is part of a mixture containing CO and steam, is
separated using an appropriate membrane reactor for this type of mixture [52].
The hydrogen from the high temperature electrolyser, which follows the combustion-to-electricity-to-
hydrogen route [49,50], is directed to the central hydrogen storage.

2.6 Carbon capture and sequestration (CCS)
Although there are other pollutants, such as SO
2
, NOx, Hg and COS, the emphasis of this system’s
design in the pollution control aspect is to address the concerns associated with increasing CO
2
emissions
[6], which are mainly associated with carbon-based solid fossil fuels. Thus, the hydrogen from various
gas streams, subsequent to cleaning and particle separation, is accompanied by CO
2
, which can be stored
[53]. Two paths for the CO
2
are envisioned here, as shown in Figure 1. The commercial route is already
applied by several industries for using and storing CO
2
in various forms. The main challenge for using
carbonaceous solid fuels in producing hydrogen is the disposal/storage of the captured CO
2
in an
environmentally feasible manner [16]. The current commercial applications include industrial use of CO
2

in supporting large refrigeration systems, making dry ice, enhanced oil recovery, and various chemical
manufacturing operations. Also some CO
2
produced in the system may be used for transporting solid
International Journal of Energy and Environment (IJEE), Volume 2, Issue 1, 2011, pp.1-38
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6
fuels into high-pressure reactors. The remaining CO
2
is sent for large-scale underground storage [54].
Such processes are being implemented commercially in recent years through a process known as
geological sequestration (GS), where the CO
2
is compressed and transported deep underground into
aquifers, depleted oil and gas reservoirs and dried underground coal beds. Some large-scale CO
2
storage
projects are already in operation and under construction, while others are the subject of feasibility studies
[55].
The future route in Figure 1 for the CO
2
storage is aimed at two strategies still at the research stage. One
involves a mineral storage where CO
2
is reacted with naturally occurring Mg and Ca containing minerals
to form carbonates. This process has several advantages, the most significant of which is the fact that
carbonates have a lower energy state than CO
2
, which is why mineral carbonation is thermodynamically
favourable and occurs naturally [56]. Thus the carbonates are stable and are unlikely to convert back to
CO
2
under standard conditions. The CO
2
recycle or reuse is another option that involves metal oxides
such as Fe
2
O
3
, ZnO and CaO to split CO
2
into CO and oxygen, for use in various processes [57]. The
latter option in which CO
2
is split into CO and oxygen is an artificial photosynthesis process; it is a
greenhouse-type concept for controlled feeding of biologically-engineered plants that can consume, in a
controlled environment, high volumes of CO
2
to store carbon and emit oxygen [58].
There is an upcoming and promising third option of disposing CO
2
, converting CO
2
into microalgae
using sunlight and water, via algae-based artificial photosynthesis. Microalgae are microscopic
photosynthetic organisms. They generally produce more of the kinds of natural oils needed for biodiesel
extraction [59]. Autotrophic algae enable photosynthesis by utilizing light (from the sun or artificial
sources such as light through fiber optic cables), CO
2
and water to grow the candidate algae (depending
on the conditions available for growth). Heterotrophic algae use thermal energy from waste heat
applications, CO
2
and nutrients derived from biogas effluents, leachate in landfills and waste water from
fermenting processes.

2.7 Planned future extensions
Two sections in the proposed system in Figure 1 are intended for a planned future extension: (i) the
upstream cleaning of feedstock (top right corner) and (ii) solids recycle coupled with a cement plant
(bottom left corner). Upstream cleaning enhances the quality of feedstock thus improving the efficiency
of various conversion processes [1] and also simplifies the separation of pollutants associated with solid
fuels [2]. Some of the envisioned upstream cleaning process are (i) using a cartridge system, where all
solid feedstocks are blended to form a uniform mixture containing a standardized composition, (ii)
treating the feedstock with solvents to clean the fuel of unusable residue, (iii) blending of high-sulphur,
high-grade coals with low-sulphur, low-grade coals and high-ash biomass (to avoid sintering), and (iv)
upgrading low-grade solid fuels with pre-treatment using heavy oils [2]. Ash is among the most recycled
solid within the system; after utilization it may be used to produce concrete blocks as part of the cement
manufacturing extension plan.
The type of conversion technologies chosen in this work for hydrogen production and CO
2
capture and
storage are based on the effectiveness of each technology, as determined by its demonstrated capabilities
from industrial and research data. Thus the system is anticipated to be capable of handling several types
of solid fuels at a given time and producing hydrogen in large quantities while delivering captured CO
2

in an environmentally and economically viable manner. As illustrated at the bottom of Figure 1,
hydrogen represents a green means of energy distribution while CCS (in red) represents the potential to
hinder the use of carbon-based solid fuels if not adequately implemented.

2.8 Status of hydrogen market in Canada
Hydrogen is mostly used in Canada at present in chemical industries. Approximately 35% of the
hydrogen use is for chemical production, 24% for refining of oil, 23% for heavy oil upgrading and 18%
for chemical process by-products [17]. Hydrogen is not yet a significant part of the direct energy system
in Canada. Most of the hydrogen used in the chemical industry is produced from natural gas by steam
methane reforming (SMR). The crude oil refining industry produces hydrogen by reforming more
complex hydrocarbons available within the refining processes [60].
Because of its large fossil fuel resources, Western Canada dominates Canadian hydrogen production.
Canada’s largest hydrogen plants are located in the oil-upgrading facilities of this region. Three plants in
Alberta and one in Saskatchewan together produce nearly 790,000 tonnes of hydrogen annually [60]. The
upgrading of heavy oil from the Alberta oil sands has recently been one of Canada’s fastest-growing
International Journal of Energy and Environment (IJEE), Volume 2, Issue 1, 2011, pp.1-38
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2011 International Energy & Environment Foundation. All rights reserved.

7
hydrogen demand sectors [15], with annual production predicted by some to rise to 2.8 megatonnes by
2020. Recent challenges to the global economies render such predictions questionable, unless economic
recoveries occur quickly. Potential future environmental limitations also can affect such predictions.
Electrolytic hydrogen production makes up an estimated five percent of Canada’s supply [60].
The amount of surplus hydrogen (hydrogen produced that is not used at the generating site) produced in
Western and Eastern Canada is estimated at 200,000 tonnes per year [60]. From an energy perspective,
this amount of hydrogen is equivalent to 760 million litres of gasoline [17] or the equivalent to fuel one
million light-duty fuel cell vehicles for a year.

3. Qualitative methodology and sustainability indicators
A qualitative methodology, which is partially quantitative, was introduced in our prior work [61], for
evaluating the sustainability of energy systems involving hydrogen production from solid fuels. The
indicators for each of the three dimensions of sustainability are chosen in this work, in the same manner
as the previous work [61], so that they are mostly independent of the indicators in other dimensions, but
related to them in the broader sense of the system’s end product – hydrogen. This is a new methodology
specific to this work in assessing the system’s sustainability within the Canadian energy market. The
methodology is developed by defining specific indicators whose values are assessed based on many other
contributions in the literature with respect to each indicator. The methodology may be applied to
sustainability assessments of similar energy conversion systems, provided appropriate variables and
indicators are specified.
The index values for each indicator are related to other indicators depending on their definitions, and
governed by the EEE platform – energy, economy and environment. The value of indices for each of the
indicators is chosen based on the collective information obtained from an extensive literature review
relating to the respective indicator. The index value ranges from 0 to 1 divided into 10 steps. Although
index values are chosen based on an examination of pertinent data and information, the assignment is
somewhat subjective. The expectations for a maximum value of 1 is kept very high in this work, so only
very few elements within the system are capable of receiving a value of 1 for some of the indicators.
The term ‘element’ in this work means a natural resource such as solid fuels, or any other unitary item
involved in the system. The term ‘process’ means an activity which involves more than one item in
making a desired output; process types considered here include conversion processes, fuel handling
processes, and carbon capture and storage processes. The term ‘system’ refers to the proposed system
shown in Figure 1.
The main product of the system, hydrogen is considered to be the most advantageous alternative fuel for
mitigating direct CO
2
emissions to the atmosphere [7] from carbon based solid fuels, while still providing
the goods and services required by society. In Canada, hydrogen is not used extensively as a fuel, but is
utilized presently in large quantities as a feedstock for various chemical processes in industries and oil
refineries.
Sustainability for the proposed system is predicted based on the assumption that a hydrogen economy
will be in place when this system is operational, which is likely at least 10 years from now [7].

3.1 Ecology indicators
In this work, ecological indicators [18] help in assessing information about ecosystems and the impact of
human activity on ecosystems pertaining to the large-scale production of hydrogen. Here the ecosystem
is considered as Canada and its energy market. Human activity involves implementation and operation of
the proposed system to obtain hydrogen in large quantities. The values of these indicators specify the
sustainability position of a particular element or process within the system along the ecological
dimension. These indicators highlight the impact of each element or process on changes to the
environment.

1. Availability:
Sustainable availability of the element within Canadian market [1-7,54,62]. The
highest value of 1 is assigned for such elements or processes that are available in the local market at
competitive price and the lowest value of 0 is assigned for lack of availability, which in the current
work is negligible since the elements and processes are selected based on minimum availability of
all of them within Canadian or American markets. For example, fossil fuels such as coals and tar
sands are mostly found in western Canada [4] and the coal market is bigger in the USA providing
International Journal of Energy and Environment (IJEE), Volume 2, Issue 1, 2011, pp.1-38
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8
ample supply for longer periods of time at very low costs. Similarly, for any process that is
commercially available, the sustainability index will be higher.
2. Adaptability:
Requiring less number of processes to acquire and process the element, minimizing
waste generation [1,3,10,17,50,51]. A value of 1 is chosen if an element or process is highly
adaptable and 0 for the least adaptable item in the system. Values for all items in the system fall in
between 0 and 1, some having higher adaptability than others based on the review of respective
elements. For example, ecological sustainability is higher for solids handling process in Canada than
for gasification process, since the former is already an established industry serving the coal power
plants in Canada [1,13].
3. Environmental capacity:
How long in terms of time and material can the global ecosystem supply
and support the element or process, without creating massive imbalances within the global
ecosystem [4,6,13,15,16,63,64]. A value of 1 is assigned if an element or process can be sustained
for a long time even with an increase in demand for it in the market place. A value of 0 is assigned if
very little resources are available in the local market and they cause a high impact on the ecosystem.
For example, a process which is capable of recycling its working materials is assigned a higher
index than a process that has less probability for reusing some of its wastes or by-products.
4. Timeline:
How new or mature is the element or process, weighted by its evolution [5, 24,54,65]
within the market place. A value of 1 denotes that a process is well established and has greatly
evolved since its creation, while a value of 0 denotes that the element is “fossilized” and the process
has little chance for further improvement in functionality. For example, commercial gasification is a
mature technology with small chance for major improvements or evolution, thus established and is
assigned a higher value (0.7).
5. Material rate:
Rate at which the element/process or products for and from the element/process can
be procured [4,12,16,62,63,66,90], accounting for the effectiveness of raw material and product
distribution networks. A value of 1 is assigned to the best network and 0 for the worst. For example,
coals have higher material rate sustainability index (up to 0.9) than biomasses (up to 0.5), due to the
well established network of mining and distribution.
6. Energy rate:
Rate at which energy can be supplied by the element or process [4,62,67,68]. A value
of 1 denotes a high energy supply rate and 0 a low energy supply rate. This indicator helps in
assessing the ecological energy density for an element or process, the amount of energy available
per unit volume of space per time period. For example, combustion processes have a very high
energy rate compared to other process due to higher rate of chemical reaction. Coals have a very
high energy rate in that they can deliver more energy per unit mass and time than biomasses.
7. Pollution rate:
The rate of pollution or emissions of any kind associated with the element or process
[1-4,16,45,56,69-71]. A value of 1 is assigned if there is very low pollution rate and a value of 0 if
there is high pollution rate. For example, consider coal use either in air combustion or oxy-
gasification. Since the technologies for pollution removal such as for sulphur compounds (SO
2
, H
2
S,
COS) are well evolved, these processes merit a higher value than for CO
2
separation and storage,
since it is still new and commercialization is yet to begin.
8. Location:
How near the element/process is from the point of use [15,50,21,27,50]. A value of 1 is
assigned if the source is very near to the point of use and 0 if it is very far (if it is outside the local
market, i.e., for this work Canada and the northern USA). The system can be placed near to the main
solid fuel source, which would be coals (which have high energy densities and still transfer more
energy with CCS than other fuels). The other elements and processes are to be moved to the
system’s geographical location, increasing the operating and maintenance costs of the system. Thus
for coals and other mine-based solid fuels, low values are assigned in this work.
9. Ecological balance:
Element or process that creates an imbalance in the local ecosystem. This
measure also indicates the level of recyclability or reuse of the element or process [68,72,73]. A
value of 1 is assigned if most of the element or process is recyclable or reusable and a value of 0 is
assigned if there is no achievable recyclability. For example, fossil fuels score a 0 in this regard
whereas renewable solid fuels such as biomass or MSW score a higher value, which depends on the
availability as well. Regarding processes, air-combustion of fossil fuels emits CO
2
along much
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9
nitrogen (thus receiving a low value due to the imbalance it causes in local energy consumption,
since higher compression energy is required for CO
2
sequestration or even for CO
2
separation).
Oxy-combustion or gasification, on the other hand, produces a relatively pure CO
2
exhaust stream,
enabling low energy capture (thus a higher value is assigned since the local energy imbalance is
minimal).
10. Endurance:
Element work load or demand factor and a process requiring equipment maintenance [1-
4,68,72,73]. A value of 1 is assigned if the element or process has high load and demand with lower
maintenance and a value of 0 is assigned when there is high maintenance irrespective of high or low
load. For elements such as fuels that require high equipment maintenance, a lower index value is
assigned for this sustainability indicator.

3.2 Sociology indicators
In this work, sociology indicators help in assessing impacts on the social system if the proposed
hydrogen system is implemented, in order to guide intervention or alter the course of social change [74].
Here the social system represents the communities within Canada that will benefit directly and indirectly
from the operation and products of the hydrogen system. The expected changes to the social system from
implementing the proposed hydrogen system are considered via the 10 indicators that follow. The values
of these indicators, which range from a high of 1 to a low of 0, specify the sustainability of an element or
process within the social system, thus helping to avoid any negative or undesirable changes.

1. Economics:
Economic and financial benefits from the element or process
[5,10,11,20,21,50,54,60,67,75-77]. A value of 1 is assigned if maximum net economic benefit
derived from the final product (hydrogen) and a value of 0 is assigned when there is a net economic
loss from transforming solid fuels into hydrogen. For example, commercial (large-scale) gasification
shown in Figure 1 provides better overall economic benefit than solar thermal gasification due to it
exhibiting a higher volume of hydrogen production in less time than is possible when using
commercial gasification.
2. Policy:
Canadian government policies and implementation trends [1,5,7,10,13,15-17,63,64]. A value
of 1 is assigned if the policies and implementation strategies support the sustainability of an element
or process and a value of 0 is assigned if they act as hindrances. Values are chosen based on
advancements in technology in dealing with energy, environment and economics of processes and
ecological sustainability of solid fuels to help in obtaining the final product of hydrogen. For
example, a government initiative to increase funding for research on biochemical routes, to produce
alternate transport fuels, helps in improving the sustainability of such processes as anaerobic
digestion [47] and algae-based biodiesel production [59].
3. Human resources:
Level of direct human work input involved in procuring, manufacturing,
installing and operating an element or process, within the Canadian market [5,70,68,72,73,90]. A
value of 1 is assigned if more human work is involved, owing to the job creation and resulting
economic benefit for the society. A value of 0 is assigned if no direct human work is involved with
an element or process. For example, solids handling processes and waste disposal involve more
human labour than primary or secondary conversion processes (except during installation and
maintenance).
4. Public opinion:
Public opinion regarding the nature and operation/behaviour of an element or
process [78-81,90]. A value of 1 is assigned if the majority of the population have a positive opinion
relating to an element or process and a value of 0 is assigned if there is a negative opinion. For
example, CO
2
emissions particularly from burning fossil fuels have been highlighted by the media
and government bodies as the main cause of a rise of mean earth’s surface temperature [6]. So, any
element or process which does not emit CO
2
or reduces it concentration in the atmosphere, is
assigned a higher value since generates positive public opinion. In the bigger picture, public opinion
often transforms into government policies, which can lead to support for measures that curb harmful
emissions, especially in Canada.
5. Environmental obligation:
Social expectations regarding the environmental obligation of an element
or a process and its by-products to be benign to the environment in which society functions
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10
[6,16,45,50,54]. A value of 1 is assigned if the operation and by-products of the element/process is
environmentally benign and a value of 0 is assigned if a process or element is necessary to the
system’s operation but is capable of harming the environment without another set of processes for
protecting the environment. This indicator encourages the elimination of any process that requires
such additional measures to protect the environment or that it be used only if no alternative can be
found. For example, converting CO
2
into biodiesel using sunlight or nutrients from the biogas by-
product associated with using algae is environmentally friendly in that it not only consumes some of
the CO
2
emitted from burning of fossil fuels but also provides an alternate transport fuel, thus
reducing additional emissions of CO
2
. So, converting CO
2
to algae is assigned a higher social index
value than other CO
2
sequestration methods that require further processes which in turn create more
ecological imbalance (underground CO
2
storage).
6. Living standards:
Impact of an element or process on human living standards (focussing on basic
requirements such as food, clothing and shelter) [54,82]. A value of 1 is assigned if an element or
process within the system improves human living standards indirectly. A value of 0 is assigned if an
element or process does not improve basic living standards. For example, coals are assigned a
higher index than biomass due to their higher energy densities, which helps in producing more
hydrogen; this in turn can provide additional goods and services compared to biomass, thereby
improving basic human living standards. Even with high energy and economic penalties for
pollution control measures, coal can still produce more hydrogen than biomass [54].
7. Human convenience:
Impact of an element or process on human convenience (higher living
standards and comforts that are not necessary like basic living standards) [54,82]. A value of 1 is
assigned if an element or process within the system helps in providing human comforts and a value
of 0 is assigned if an element or process does not provide human comfort, through additional
hydrogen production. The index values for solid fuels are similar to those for the previous indicator
(#6). But for some processes, the index value may be lower, e.g., if more fuel is used due to
increased secondary and environmental protection process loads in producing hydrogen.
8. Future development:
Possibilities for future economic and social growth based on the nature of an
element or process [1-6,60,67,75-77]. A value of 1 is assigned if using the element or process
increases the possibility for societal development. A value of 0 is assigned if using the element or
process within the proposed system does not provide opportunities for societal development, even in
the local community. The system involves many processes that produce several by-products in
producing hydrogen. These are given higher index values since the by-products help in increasing
the overall economic and social income to the local community.
9. Per capita demand:
Impact of population/customer demand on producing hydrogen with the element
or process, affecting the ability to carry out the process sustainably [6,54,82]. A value of 1 is
assigned if fewer industries use the element or process, thereby increasing market availability and,
possibly, price competitiveness. A value of 0 is assigned when the element or process is used by
many industries, which hinders availability and can reduce sustainability. For example, coals are
mostly used for power generation and in steel industries, based on its per capita availability it is
assigned a high value. But biomass per capita availability is small and is mostly used in co-
combustion processes or as manure, reducing the per capita demand sustainability index.
10. Lobbying:
External influences on the impact of an element or process, through political and
economic lobbies, that can affect government policies related to sustainability
[16,17,54,63,65,66,83]. A value of 1 is assigned if the process or element has effective lobbying and
a value of 0 is assigned if no lobbying is attempted. Negative lobbying is not considered at this
point. For example, the coal industry is well established economically and is engaged in political
lobbying to maintain its use within the Canadian energy market and to promote government policies
that support the coal industry [83]. In recent years, green energy programs have received extensive
lobbying due to their potential long-term contributions in mitigating global warming. So, elements
or processes associated with green energy policies (such as anaerobic digestion, plasma gasification,
supercritical water gasification, CO
2
to algae) are assigned higher index values.


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11
3.3 Technology indicators
In this work, technology indicators help in assessing the knowledge, design, performance and production
aspects of an element or process selected for the hydrogen system, providing an engineering perspective.
The indicators are chosen so that they assess the technical capabilities of each element in the system on
the same level. The values of these indicators specify the sustainability of the system and its components,
such that the technologies chosen are examined for energy affordability, environmental limitations,
commercialization possibilities and potential progress with respect to the production of hydrogen.

1. Net energy consumption:
Energy requirement of the element to bring it to the point of use and
energy required for operation of processes [20,24,30,31,36,39,51,54,60,68,76,82]. A value of 1 is
assigned if the element or process requires little energy and a value of 0 if it requires a great amount
of energy. For example, processes that generate energy have higher index values (primary
conversion, electricity generating and hydrogen production processes) than those that consume
energy during their operation.
2. Exergy:
Relative exergy of the element or process with respect to the system and the environment
[54,62]. A value of 1 is assigned for an element with high exergy or for a process that has lower
exergy destruction and a value of 0 is assigned for an element with low exergy or for a process with
high exergy destruction. For example, combustion processes have high exergy destruction compared
to gasification processes and subsequent hydrogen production processes. Thus combustion
processes within the system are assigned lower technology index values for exergy.
3. Efficiency:
Efficiency (ratio of desired output to input, considering both energy and exergy) of
every element or process and related technology in obtaining the final product of hydrogen
[68,72,73]. A value of 1 is assigned for processes that have very high efficiencies (above 0.9) and a
value of 0 is assigned for processes that have very low efficiencies (below 0.1). For example,
commercial electrolysers have between energy efficiencies ranging typically from 0.5 to 0.7 [54]; a
value of 0.7 is assigned to them, which is the highest value for efficiencies of all the items in the
system.
4. Design:
Impact of design of a process or an element on sustainable operation of the system [7,10-
13,17,22,25,50]. A value of 1 is assigned for the best design, taken to be a design that, among other
factors, improves the overall performance of the system and minimizes waste generation. A value of
0 is assigned for the worst design of a process. No process or element in the current work is assigned
a value of 0 is given the types of processes selected for inclusion in the system design. For example,
consider USS gasification, which is still in the research phase but has significant future potential.
This process is assigned a low index value (0.3) since it is not a fully mature design and is likely
while it develops to cause problems in the overall system or with other conversion processes in it.
5. Research:
Impact of research on future developments of a process or an element that affect the
ability of the system to produce hydrogen sustainably [7,10-13,17,22,25,50,54]. A value of 1 is
assigned for an element or process with high probability for successful research and a value of 0 is
assigned when there is a low probability for research and advances. For example, utilities like solids
handling and ash and slag collection have a low probability for intensive research that will help in
improving the system’s performance, so they are assigned a lower index value. For plasma
gasification and CO
2
-to-algae conversion processes, the amount of research, due to technology
prospects and incentives, is sufficient to merit higher index values.
6. Demonstration:
Capacity for demonstration of the impact of an element or a process in contributing
to hydrogen production in the system [3,54,60,84,85,86,87,88]. A value of 1 is assigned if the
process or element is has already been demonstrated (as for commercially established technologies).
A value of 0 is assigned if there is a need in the future for demonstration to establish the capability
of the technology. For example, commercial gasification and solids handling processes have high
index values since they are more mature than the ones that are still undergoing research and
development, such as CO
2
-to-algae conversion processes, supercritical water processes and USS
gasification.
7. Commercialization:
Potential for process or element technology to become commercially viable,
enabling sustainable large-scale operation within the system [1-5,11,13,24,34,51,54]. A value of 1 is
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12
assigned for processes or elements with excellent potential for commercialization and a value of 0 is
assigned for processes with little potential for commercialization. For example, USS gasification is
assigned a low value (0.4) since it has very limited potential for commercial development due to
size constraints (i.e., large-scale operation will result in very low efficiencies thus increasing
operating costs). Commercial gasification is assigned a high value (0.9) since it operates
commercially on a large-scale and is the fastest growing segment within the coal industry due to its
ability to produce synthetic gases for various alternative fuels programs [51].
8. Impact:
Impact of actual process or element on sustainability of the system for producing hydrogen
[11,13,20,34,36,41,46,47,54,67,68]. A value of 1 is assigned to processes or elements that have very
high impact on the system’s performance and a value of 0 is assigned to those that have very low
impact. For example, within the commercial gasification process (Figure 1), the air separation unit
(ASU) is assigned a higher value (0.8) than the ash handling system (0.4) because the ASU is
crucial to a high-efficiency solid-to-gas conversion as well as effective downstream CO
2
capture.
The ASU therefore has a significant impact on improving the overall efficiency of the system for
producing hydrogen, whereas the ash handling system, although essential, does not impact the
system efficiency as much as the ASU.
9. Evolution:
Capacity for process technology to improve, adapt and grow in the Canadian energy
market place [4,5,7,10,13,54,63,70,83]. A value of 1 is assigned to processes that have high
opportunities for evolving to increase in efficiency and decrease in operating and maintenance costs,
while a value of 0 is assigned to processes with little opportunity for such development. For
example, commercial gasification has very little chance for evolution and is thus assigned a lower
value (0.3), whereas supercritical water gasification is assigned a high value (0.7) since it is is
expected to evolve into an efficient process for large-scale hydrogen production that is useful for
effective disposal of sewage water [46].
10. Environmental limitations:
Limitations of process technology arising from harmful impact on the
environment while operating within the system [6,15-17,35,45,50,86,89]. A value of 1 is assigned to
processes with few limitations in operation due to damage caused to the environment, while a value
of 0 is assigned to the processes with high limitations in operation due to their environment impacts.
For example, devices that contribute to pollution control within the system, such as the ash collector,
syngas cleaner and membrane separator, have high index values since they are subject to few
environmental limitations in their operation and they contribute to environmental preservation.

4. Sustainability of system components
The first set of results or sustainability index values are described for different components within the
proposed system in Figure 1. The sustainability indices are plotted figures 2 to 8 on a percentage basis
for different aspects of the proposed system, as sustainability triangles with three axes: techno-, eco- and
socio-centric. The index values for elements such as each solid fuel are averaged across the 10 indicators
in each sustainability dimension. For more complex devices like conversion processes (gasification,
anaerobic digestion, etc.), the average index value of all the components within the sub-systems or
processes is evaluated first for each indicator and then averaged across the indicators within each
dimension. The maximum value for the sustainability indices in figures 2 to 8 is less than 0.8 (i.e., 80%).
The averages are evaluated as simple means. Averaging sustainability indices may not provide the exact
impact on system sustainability of indicators and system components, but it does provide a broad
understanding of the impact on the sustainability of the system.
The values for each of the specific indices are shown in Tables 1 to 3 in the appendix. Discussions within
each dimension for every indicator are based on the index values in Tables 1 to 3.

4.1 Sustainability of coals
Since coals are already an established fuel for the electricity market, its sustainability is above average.
Of the total coal supply in Canada, 77% is used for electricity generation [4] in over 60 coal combustion
power plants [1] totaling over 17 GW of electricity generation capacity. Of this capacity, 44% is located
in from Ontario, 34% in Alberta, 10% in Saskatchewan, 7% in Nova Scotia, 3% in New Brunswick, and
1% in Manitoba, based on data for the year 2004. About 8% of the coal supply is used by industries for
coking and gas manufacture. Based on Canadian coal reserves [16], the potential applications for coal are
International Journal of Energy and Environment (IJEE), Volume 2, Issue 1, 2011, pp.1-38
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13
not being realized currently beyond electricity generation and limited industrial use [90], because of the
existence of natural gas and crude oil resources which have a higher market value than coal and are in
demand in external markets.
From Figure 2, it is evident that all coals have less than average ecological sustainability, with anthracite
at about 31%. This is largely due to lower environmental capacity exhibited by coals and the ecological
imbalances their use can cause. All coals have the same values for techno- and socio-centric dimensions.
Within the ecological dimension, coals score high (about 70%) in availability, material rate and
endurance and low (less than 20%) in adaptability, pollution rate and ecological balance. Industrial
residue is a mix of inorganic solid wastes from various industries that may serve as fuel in combination
with coal or biomass. Industrial residue is assigned higher index values in terms of pollution rate and
ecological balance.
Within the sociological dimension, coals are assigned high scores for per capita demand and lobbying
and low scores for public opinion and environmental obligation. Industrial residue scores the highest for
future development and the lowest for lobbying, and has an average index value of 47%.
Within the technological dimension, coals score high on exergy and technology impact do not receive
low index scores for any of the indicators, all of them being above 50%. This result demonstrates the
characteristics of industries associated with coals: power generation, steel manufacturing, and oil
companies (at least in western Canada).

0
10
20
30
40
50
60
70
80
ECO‐CENTRIC
SOCIO‐CENTRICTECHNO‐CENTRIC
Anthracite coal
Bituminous coal
Sub‐bituminous coal
Lignite or Brown coal
Industrial residue
Fossil
inorganic
solidfuels


Figure 2. Sustainability indices (%) for solid fossil fuels and inorganic fuels used in the system

4.2 Sustainability of biomass
Biomasses are used in co-firing and co-gasification applications in Canada. Few units converting
biomass and MSW to electricity are in operation in Canada, with less than 50 MW of electrical
generating capacity [60,67]. These plants produce less than 5% of the total electrical energy used in the
province of Ontario. This low utilization is due in part to a lack of higher conversion potential with
biomass fuel, because only one energy conversion technology is used at a given time within the facilities
operating in Canada.
Figure 3 shows the averaged sustainability triangle for all the biomasses and system solid wastes (solid
wastes that are generated after primary and secondary conversion processes within the system). Biomass
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14
from farms are assigned a higher index value (10% higher) than biomass from forests, due to a higher
average score in techno-centric dimensions. This result is mainly due to the nature of the feedstock,
which is drier and bulkier than forest biomass, thereby enabling higher values for evolution, commercial
and net energy consumption indicators.

0
10
20
30
40
50
60
70
80
ECO‐CENTRIC
SOCIO‐CENTRICTECHNO‐CENTRIC
Biomass, Forest
Biomass, Farm
Energy Crops
MSW, Sewage
MSW, Garbage
System solid  wastes
Renewable
solid
fuels


Figure 3. Sustainability indices (%) for renewable solid fuels used in the system

Within the ecological dimension, farm biomass, energy crops and MSW-garbage have the same average
index values. MSW-sewage has a lower value due to low index (10%) for adaptability, pollution rate and
ecological balance. System solid wastes have very low indices for all dimensions since they have the
lowest energy rate, economics and exergy.
Within the sociological dimension, MSW-garbage has a 10% lower value than biomasses, since
biomasses have high values (over 70%) for economics, public opinion and lobbying. The characteristics
of system solid wastes cause them to receive very low values for all indicators in this dimension. By
recycling these system wastes, the sustainability of waste management can be improved. In future waste
handling regulations will likely become more stringent, making it worthwhile to improve sustainability
now.
Within the technological dimension, most of the biomasses are similar and are assigned the highest
values of all the three dimensions. This is due to the above-average values scored by biomasses, energy
crops and MSW-garbage. Energy crops are assigned the highest value (90%) for environmental
limitations in the use of technology relating to its processing.
The overall sustainability score of biomasses can be expected to increase once a market and demand are
established.

4.3 Sustainability of fuel handling processes
Solid fuels arriving at the system require temporary storage, drying, crushing/milling and internal
transport mechanisms. The handling of solid fuels consumes some energy with operation and
maintenance costs and is vital to the functioning of a system using solid fuels. Due to the availability and
widespread use of solid fuels [91], their handling is mature. Upstream processes (in Figure 1) involve
cleaning, blending and upgrading of solid fuels to enhance the quality of the feedstock, thus improving