Design for the Environment/Hydrogen Production

This page is a part of Design for the Environment course

Electricity, Solar Power Generation, and Renewable energy generated from natural resources are one of the few methods of energy production that will dominate the world’s energy systems in the near future. The usage of Hydrogen is one such example. Hydrogen is known as an environment friendly fuel that combines with oxygen to produce energy in the form of heat. Today, 50 million metric tons of hydrogen is being produced on annual basis, most of which is employed in industrial and chemical industries. The world is gearing towards optimizing its energy production. Hence, it is anticipated that majority of the countries will shift their energy usage towards hydrogen economy, thereby increasing the demand of hydrogen production in the future.

This report aims at comparing the characteristics of the two proposed alternatives (Solar electrolysis and Thermochemical Decomposition of Water) to the baseline alternative (Stream Methane Reforming) and evaluating the economic and environmental impacts of each. To achieve this, a set criterion is established to compare each alternative by selecting a potential client. The client for this report is a fuel cell company that aims at fulfilling the fuel requirements of the buses operated by Toronto Transit Commission. There are a total of 1799 buses owned by TTC according to the 2007-operating statistics, which cover a total distance of approximately 110, 684, 880 km per year. According to the current economy a bus travels approximately 16 km per kg of hydrogen and the energy density of hydrogen is 143 MJ / kg. Using the given figures TTC buses require approximately 6,917,805 kg of hydrogen annually. The report focuses on the demand for fuel established above and the environmental impact of each process to achieve this demand.

The analysis of each process was divided into the following five components


 * 1) Functional analysis
 * 2) Streamlined Life Cycle Assessment (SLCA) - Qualitative Environmental Impact
 * 3) Economic input-output life cycle assessment (EIOLCA) - Quantitative Environmental Impact
 * 4) Cost analysis
 * 5) Societal analysis

Project Information
Section 2, Group B22

Mohammad Saad Khan (immsk)

Brendan McDermott (brendanmcdermott)

Arsalan Samdani (arsalan_samdani)

Qazi Wajahat Sohail (wajahat87)

Highlights and Recommendation
Processes

Three processes for the production of Hydrogen are being discussed namely Steam Methane Reforming, Solar Electrolysis and Thermochemical Decomposition of Water. In Steam Methane Reforming (SMR), methane reacts with steam to yield Hydrogen and Carbon dioxide. The reaction occurs in a series of steps with Fe2O3–Cr2O3–CuO and CuO– ZnO–Al2O3 as catalyst beds.

The Solar Electrolysis process, on the other hand, involves use of photovoltaic cells to convert sunlight into electric energy. Electrolysers then utilize this energy to electrolyze water into pure hydrogen and oxygen.

Lastly, Thermochemical Process utilizes the heat energy obtained from Generation IV nuclear reactors, to split water into hydrogen and oxygen using S-I Thermochemical cycle.

Performance

Each of the three alternatives are ranked on a scale ranging from zero to five on the basis of their performance in each process stage analyzed in the following sections. Each process stage is assigned a weighting factor depending on its significance in relevance to the report. Environmental impacts, being the most important factor in hydrogen production, are assigned a combined weighting factor of 0.50. Cost impact is the second most important factor with a score of 0.25 followed by function and societal impact having a weight factor of 0.15 and 0.10, respectively. The weighting factors add up to 1.00. The total score for each alternative is the sum of individual score multiplied by its associated weighting factor.

Steam Methane Reforming is the most efficient and economical option to obtain Hydrogen at large-scale, with an efficiency of 65-75%. Also, SMR is an established technology being employed all across the world to generate hydrogen for industrial and commercial use. However, the major drawback of this technique is its dependence on extraction of non-renewable and limited natural gas resources. Further, the emission of carbon dioxide as a byproduct accounts for as much as 25% of greenhouse effect, which calls the need for an alternative technique.

Solar electrolysis technique, the first potential alternative to SMR, has a complete lack of material inputs and negligible emissions associated to it, with water being the only input and Hydrogen and oxygen being the only products. However, the major set back is the high capital and environmental cost, as evident from table 1, required to setup the entire infrastructure.

Lastly, Thermochemical Decomposition of Water, which is the second proposed alternative, is an efficient method as it requires minimal input of raw materials. Apart from water, iodine is utilized which can be recycled and reused. Also, the heat energy required to produce hydrogen is achieved from already existing nuclear plants, which ensures a low operating cost. However, like the solar electrolysis method, it has a high capital and distribution cost associated to it, but according to Guthrie method the cost per unit of hydrogen descends as the production capacity of Thermochemical plant increases.

Recommendation

It is evident from the analysis that Thermochemical process is a technically feasible method for hydrogen production. The cost per unit kg of hydrogen is reasonable as compared to solar electrolysis method and carbon and other toxic emissions are minimal unlike the steam methane reforming process. Further, the cost per kg of hydrogen will decrease by a considerable amount when the production capacity of thermochemical plant increases to 200 tonnes per day. Hence, thermochemical process is a reliable method for large-scale production of hydrogen in the near future.

Steam Methane Reforming
Looking at the various hydrogen generation methods that currently exist and those that are being proposed, it seems that Steam Methane Reforming presents a greater possibility for optimization as it is a mature technology having been in use for many years now.

The raw materials used in Steam Methane Reforming are as the name indicates methane and steam. Before the steam reforming process can take place the natural gas has to go through a purification process in a hydrogenation vessel in order to remove sulfur impurities. A small amount of hydrogen is used from the product stream for this. The product of this process, H2S gas, is then removed in a ZnO bed. The essence of the process is taking purified natural gas (methane) and reacting it with steam at a high temperature (700°C -1100 °C), this process takes place over a nickel-alumina catalyst: CH4 + H2O → CO + 3 H2. The Carbon monoxide produced is then reacted with steam at 2.6 MPa over a catalyst, in a two-stage process known as water gas shift, to produce hydrogen and Carbon dioxide. CO + H2O → CO2 + H2. Water gas shift occurs in two stages called high temperature shift and low temperature shift, a reformer can be designed to work on only one of the stages, but it’s been observed that incorporating both the stages improves efficiency and increases the amount of hydrogen produced. These shift reactions use two sets of catalysts in two stages, the first stage known as the High temperature shift uses a Fe2O3–Cr2O3–CuO catalytic bed; the second low temperature shift stage uses a CuO– ZnO–Al2O3 bed The reactions can thus be summarized as: CH4 + 2H2O → CO2 + 4H2.

This project is addressed towards the Toronto transit commission (TTC) as mentioned above, the TTC would require about 6.9 million Kg/year, the plant being proposed in this analysis would be able to produce 8.5 million kg/year. Hence initially the plant would be operating at below capacity but in time, as the TTC fleet expands, the extra capacity will be made useful.

Solar Electrolysis
An alternative method for obtaining hydrogen from water is solar electrolysis. In this method, solar energy is collected and then converted into a standard alternating current (AC) electric current. This current is applied to the water with the intent of splitting the water into pure hydrogen and water molecules.

H2O + 0.079 kWh → H2 + 1/2 O2 (in the presence of aqueous KOH as an electrolyte)



One of the most attractive features of the solar electrolysis process is that it requires virtually no inputs and emits virtually no waste emissions. There is a small carbon footprint when converting the solar energy collected by the silicon based photovoltaic cells, into AC electricity. There is also an input of KOH during the electrolysis process, as the water requires that an aqueous electrolyte be introduced in order to split when the current is applied.

As indicated above, the prospective client for this process would be the TTC. With the required hydrogen production being 6.9 million kg/year, the solar electrolysis process would require that 1.29 GWh of electricity be generated each day in order to meet quota.

It is this figure that provides the prohibiting factor to implementing a solar electrolysis system. With current solar cell technology, PV cells operate at approximately 25% efficiency. This factor, along with the fact that the cells must be exposed to at least 5 hours of direct sunlight each day, make the potential for failure to provide 1.29 GWh/day very high. Furthermore, the cost to manufacture and install the required amount of solar cells would be extremely high (likely prohibitive in the current economic climate).

Thermochemical Decomposition of Water
One method of obtaining hydrogen from water is through the thermochemical decomposition of water. High temperature heat drives a thermochemical cycle to split water into hydrogen and oxygen. The nuclear energy driven thermochemical hydrogen production is a process in which waste heat from Nuclear reactors is used to provide the necessary heat to drive the thermochemical cycle.

It is envisioned for the generation four nuclear reactors to be able to discharge high temperature heat (700°C -1200°C), which would be sufficient to drive this thermochemical process. One example is the Very High Temperature Gas-Cooled reactor, which uses helium gas instead of water as its reactor core coolant. The helium gas is able to carry very high temperature heat in large amounts. It would cool the reactor core and in doing so, store enough thermal energy to drive the reactor turbine for electricity generation and also drive the thermochemical cycle for hydrogen production.

The Sulfur Iodine Cycle is one of the proposed thermochemical cycles for large-scale hydrogen production. Water is decomposed in the presence of Iodine and Sulfur dioxide. A large inventory of these chemicals is required initially. Sulfur dioxide and Iodine are introduced to the cycle as catalysts and at the end of each cycle the amount spent is reacquired and reentered for the next cycle. The cycle consists of the following three stages :

STAGE 1: Iodine and Sulfur dioxide react with water at 120°C to produce Hydrogen iodide and Sulfuric acid.

I2+ SO2 + 2 H2O → 2 HI + H2SO4 (120°C) STAGE 2: The Sulfuric acid acquired in stage one is decomposed at a high temperature of 830°C to obtain Sulfur dioxide,water and oxygen.

2 H2SO4 → 2 SO2 + 2 H2O + O2 (830°C)

STAGE 3: Finally, the Hydrogen iodide from stage one is decomposed at 450°C to produce iodine and hydrogen. Thus the amount of   Iodine spent in stage one is reacquired. 2 HI → I2 + H2 (450°C)

Streamlined Life Cycle Assessment
In Streamlined life cycle assessment (SLCA) each alternative is scored in twenty-five different categories pertaining to five life cycle stages of the process and its five environmental impacts. Each category is assigned a rank from zero to four based on the environmental impact that a specific process had relative to the other two and an explanation is provided to justify the ranking. Hence, SLCA provides a qualitative analysis, in printed and tabulated form, of the life cycle for each process

Process Legend for Table 2

SE - Solar Electrolysis SMR - Steam Methane Reforming TDW - Thermochemical Decomposition of Water

Steam Methane Reforming
As can be seen from the SLCA Table 2 above resource provisioning is the most environmentally detrimental stage of the lifecycle of a Steam methane reformer this is because of the heavy environmental impact of extracting and transporting natural gas. In the process implementation stage the steam methane reformer fares comparatively better, construction which is the main activity carried out in this stage requires large amounts of energy and the materials required for construction such as concrete and steel need raw materials that are extracted from the earth. It is in the primary process implementation stage, where the largest amount of carbon dioxide emission takes place. The catalysts used during this stage require trace metals and even though the quantities used are small their extraction results in significant environmental impact. The end of life stage involves the demolition of the plant and the disposal of the products of demolition, since the main material used in construction is concrete and as is usual this concrete ends up in landfills. The steel, on the other hand, can also be recycled, but there is considerable energy expended in this process.

Solar Electrolysis
The first two stages of the SLCA for solar electrolysis of water have the worst effect on the environment, as can be seen on the chart above. This is due to the current lack of infrastructure in place to contain this process. In order to implement a solar electrolysis system on the desired scope, a solar energy collection field must be installed, power lines constructed from there to the electrolysis station, water pipelines laid to the electrolysis station, and factories to manufacture all necessary components must be constructed.

In the Resource Provisioning Stage, all virgin materials must be extracted from the earth by a variety of mining processes. This requires material and energy inputs, and produces a large quantity of waste material in the form of solid and liquid slag, and greenhouse gases. In the Process Implementation stage, all components, machinery and infrastructure must be manufactured and installed. This stage uses all the virgin materials from the previous, and additionally has a large energy input from the factories used in the manufacturing process. Further, there is a great deal of waste output from the various factories, as well as a further gaseous output from transporting components to their installation site.

It can be seen from the above chart that the Primary and Secondary Processes (solar energy collection and hydrolysis of water) are completely clean processes. They require no inputs in the case of energy collection, minimal input in the case of electrolysis and have only negligible harmful outputs. The majority of the components in the solar hydrolysis process are recyclable or reusable as well.

Thermochemical Decomposition of Water
Table 2 shows that the Resource Provisioning and Process Implementation stages pose the greatest environmental concerns in the thermochemical hydrogen production life cycle. This is due to the large quantity of chemical inventory required to initiate the process. Energy is consumed in the extraction, processing and transportation of Iodine and Sulfur to the plant site. Apart from that, carbon steel and nickel are required in high quantities along with other construction material for the implementation of the process. Extraction and processing of these fossil resources leaves a considerable impact on the environment.

The Primary process of the nuclear driven thermochemical cycle is an attractive feature of the plant. The process uses Iodine and Sulfur to decompose water. The only two outputs of the closed cycle are oxygen and hydrogen. The energy used is the waste heat discharged from the nuclear reactor, and therefore there are no major emissions related to the operation of the plant.

JAEA has given recommendations for an S-I thermochemical process for the Japanese HTTR, and it has been decided that the thermochemical plant would be built as a non-nuclear grade chemical plant. Therefore the decommissioning and disposal concerns for the nuclear reactor facility would not apply to the thermochemical plant.

Economic Input-Output Life Cycle Assessment


Economic input-output life cycle assessment (EIOLCA), developed by the Green Design Institute at Carnegie Mellon University, estimates material and energy resources and the environmental impacts resulting from economic activity. To use this methodology, either in hybrid or custom mode, the total annual direct (capital, operating and disposal) and indirect (environmental, societal)costs serve as the input to analyze the environmental effect. For our analysis, we consider the impacts of Resource Provisioning and Process Implementation and Primary Process stages on GWP, SO2 emissions and Energy use for each alternative. Further, the total primary process operation costs over the life span of the plant are considered to achieve a fair analysis. The Data obtained from EIOLCA analysis was used to plot comparison charts for each alternative which are provided in figure 4 and 5.



Steam Methane Reforming
This analysis has been conducted over the lifetime of the Steam methane reactor, for the three main stages of the life cycle i.e. Resource Provisioning, Process implementation and Primary Process Implementation stages. From the above table it is clear that most impacts are caused during the Resource Provisioning stage, the reason for this is that during the resource provisioning stage large amounts of Natural gas are used, and as was mentioned in the Streamlined Life Cycle Analysis, the extraction and transportation of natural gas are very environmentally stressful. The primary process operation stage and Process implementation stage are not as environmentally stressful hence to optimize the environmental impacts of this process over its life cycle; research needs to be done on developing better methods of Natural gas extraction and transportation, methods that are more Energy efficient, and less environmentally damaging.

Solar Electrolysis
Unlike steam reforming and thermochemical decomposition, only two stages of the solar electrolysis are necessary to complete an EIOLCA. The primary process for solar electrolysis (production of solar energy and electrolysis of water) is a clean process. The amount of pollutants and waste materials produced are negligible when compared to the outputs from the Resource Provisioning and Process Implementation stages.

During the Resource Provisioning and Process Implementation stages, the greatest contributor to GWP, SO2, and energy use, is the power generation sector. This indicates that it takes a great deal of energy to operate the equipment and systems required to extract the raw materials from the earth and manufacture them into the required solar electrolysis infrastructure and components. From a deeper analysis of the EIOLCA generated for the solar electrolysis process, it is revealed that the power generation and supply sector is the major contributor to almost all toxic releases. The most notable exception is the CO output, which has Truck Transportation as its primary contribution.

In general, even during resource provisioning and process implementation, it can be seen that solar electrolysis poses a lesser environmental impact than steam reforming and thermochemical decomposition.

Thermochemical Decomposition of Water
The comparison in the above table gives us an idea of how different stages of the life cycle contribute to GWP, Energy demand and SO2 emissions. It is clear from the data that the primary process operation sector is the largest contributor to all three environmental outputs considered. This is a very logical result,considering that the amount of emissions and energy consumption accumulated as a result of energy requirements and maintenance activities over the assumed 30 years life span of the plant.

Resource provisioning and Process implementations have a considerable impact on the GWP factor. This is due to the extensive extraction and processing of iodine and sulfur inventory, and of carbon steel and nickel required for construction.

Steam Methane Reforming
The cost of the hydrogen obtained from a steam methane reformer is highly dependent on the price of natural gas in the market. Other major costs that contribute to the price of hydrogen are the capital costs and operating costs of the reformer. The plant considered in our analysis is based on a model created by the US department of energy to analyze the feasibility of transitioning to a hydrogen based economy. It needs to be pointed out that the costs detailed in the analysis carried out by the US department of energy are for a plant located on the US gulf coast hence there will be difference in costs when setting up the plant in Canada. The scope of this cost analysis is limited to production and storage of hydrogen on site, a much more detailed analysis that includes the cost of setting up hydrogen distribution stations among other things, needs to be considered to get the true cost of hydrogen to the consumer.

Solar Electrolysis
The cost of implementing and running the solar electrolysis process depends most highly on the cost to produce and install the solar cells. At twenty-five years, solar cells have the shortest life span of all the components, so the replacement costs for this system would be fairly low. This cost table cannot be taken as a set-in-stone price quote, as it relies on several assumptions. For instance the cost of solar panels is predicated on the assumption that the panels are able to receive five hours of direct sunlight each day. Under this assumption and current technologies, hydrogen could be produced through solar electrolysis for $4.09/kg, a cost much higher than that for steam reformation or thermochemical decomposition.

Thermochemical Decomposition of Water
We have assumed in this analysis a thermochemical hydrogen generating plant comprised of four units rated at 600MWt each with a 42% thermal efficiency (4200mol/reaction rate). The main economic concern for this process is the high costs of capital related to it. Approximately $269,000,000 in capital investments is required to implement the thermochemical cycle for large-scale hydrogen production. This is mainly due to the large amount of Iodine inventory required to initiate the reaction process, carbon steel and nickel required for construction, as well as the engineering that goes into the complex plant design. According to the Guthrie method of estimating costs, for chemical plants the cost per unit of capacity decreases with increase in size. Therefore the plant capacity will have to be large enough in order to be able to produce hydrogen at a competitive cost. Due to the large cost of capital for the implementation of this process, a production capacity of less than 50tons/day would not be cost effective. Since waste heat from a nuclear reactor drives the thermochemical cycle,the operation of the process is comparatively more economical. Operating costs are primarily dominated by the cost of production of ultra pure water. An estimated amount of 1,917 million kg/year of ultra pure water is required for the production capacity under analysis. Therefore at a rate of 8cents/kWh, the estimate electricity cost to acquire the desired amount of ultra pure water in US dollars is approximately $2,000,000. At a production level of 150tons/hour, the cost of hydrogen in US dollars is estimated to be 2.01$/kg.

Steam Methane Reforming
Steam methane reforming is an economical and a technically feasible means of generating hydrogen. But the question one needs to ask is, will it end our dependence on fossil fuels? The answer to this question is no, using natural gas as a feedstock, steam methane reforming will only shift the source of carbon emissions from the fossil fueled vehicles to the Hydrogen generating facility. This does not mean that Steam methane reforming has no place in the future hydrogen economy, in fact Steam methane reforming can play a very crucial role in helping us transition to a hydrogen economy, until cleaner more economical ways of generating hydrogen can be found. In terms of emissions the major emissions given out by the plant itself are Carbon dioxide emissions; with the ongoing research in carbon sequestration techniques there is a possibility that a viable solution to this emission problem will be available in the future. As with any industrial project, setting up a steam methane reformer would bring it with issues concerning noise and visual pollution a possible solution to this problem would be to locate the facility in an industrial zone, away from the city.

Solar Electrolysis of Water
Current trends in public thinking show a recent shift towards environmental consciousness. One of the most popular aspects of this is operating automobiles using hydrogen as the fuel. With this in mind, the idea of a perfectly clean process to produce hydrogen, and using that hydrogen to operate buses should be a project that would be responded to in an extremely positive manner. However, the cost to implement this system would be so high, and the fact that the TTC would have to retrofit their entire fleet of buses to run on hydrogen, there would be a drastic increase in TTC prices. Logically this increase would be a minimum of 100%, as hydrogen costs twice as much to produce (by distance traveled) than does gasoline. This price increase would be considered unacceptable by the TTC riders.

Thermochemical Decomposition of Water
The two attractive features of the thermochemical hydrogen production cycle are that it runs on waste heat from a nuclear reactor and it uses water instead of fossil resources to produce hydrogen. Therefore, the large-scale production of hydrogen using this process would be welcomed.

That having been said, since high temperature nuclear reactors are required to run the process, and the development of this technology still requires more research and experimentation, the general public might not welcome nuclear trials for the swift implementation of new nuclear designs. Nuclear technology has been criticized in the past due to the devastating effects as a result of accidents such as the Chernobyl incident in 1986. It has also been discovered recently that the French government’s nuclear experiments have had diverse effects on people living in the vicinity of the trial sites. Such incidents do a great deal of negative publicity for nuclear technology. Nuclear experiments have never been widely welcomed by the general public and hence this might pose a great obstacle in conducting large scale experiments for advanced nuclear reactors. This would delay the implementation of advanced nuclear reactors for hydrogen production.