Design for the Environment/Hydrogen Generation Methods

Hydrogen has been seen as one of the most suitable alternative energy source, and many researches and developments are being conducted in improving the production efficiency and production cost for hydrogen. However, it has been studied that while a generation method brings high production efficiency, it also brings many negative environment impacts. Therefore, being able to determine a balance between production cost and environmental cost is essential in making hydrogen generation method decision. In here three different hydrogen generation methods are introduced and analyzed: Steam [Methane Reforming - currently the most common way of generating hydrogen, it generates hydrogen through steams and methane, has a very high production efficiency as well as high pollutant release. Electrolysis - is also commercially used, hydrogen is produced by splitting water molecules through a reaction process with the electrically conducted special metal, this hydrogen generation process releases less pollutants, but also has a lower production efficiency. Photocatalytic Water Splitting - which is a hydrogen generation method that is still in the research stage, this method also produce hydrogen by splitting the water molecule, but it uses solar energy as its reaction energy source, it has very low pollutant release and poor production rate. Analysis and comparison are performed based on the following topics: Functional Analysis: Introduced the techniques used and background to these different hydrogen generation methods, its advantage and disadvantage are also discussed. Economic Input-Output Life Cycle Analysis (EIOLCA): Each hydrogen generation methods’ environmental impacts over its lifecycle and supply chain are analyzed. Streamlined Life Cycle Analysis (S-LCA): Detail environmental impact during the production process for each hydrogen generation methods were analyzed and given a score matrix consist of 25 topics. Each matrix was given a score from 0 to 4, where a higher score means more environmental friendly, and explanation to the score determination. Cost Analysis: Life cycle cost, financial analysis, and indirect costs of each method are performed. Societal Analysis: Qualitative analysis on other issues that do not belong to the categories described above; such as noises, public preferences and values...etc. Data and information acquired for the analysis above are as if these three hydrogen generation plants are all based in Arizona, USA, at where has the highest sun absorbance across United States. United States was chosen because many of the information and data on these hydrogen generation technologies and analysis tools (EIOLCA, S-LCA) are US based.

 Project Information

Section 02: Group 9B

 Group members  Yu-Hao Tseng (howard12f) Tsz Yeung Lo (travislo) Arthur Cheuk (arthurcheuk) Denushka Sarathchandra (Sarathc2)

Highlights and Recommendations
Based on the five analyses summary of these three hydrogen generation methods, a score matrix is given below, where each score is assigned based on its performance within each category.

Steam Methane Reforming, with easy access, cheap methane supply, and its high hydrogen production rate – 83%; a lot higher in comparison with the 50%, and 12% from Electrolysis, and Photochemical Water Splitting; scored full point even though it produces large amount of CO2 and other pollutant during its chemical reaction for generating hydrogen. Electrolysis and Photochemical Water Splitting produce hydrogen through similar chemical reaction of re-usable special metals and water, results in a much cleaner production process. Therefore, at this stage, Steam Methane Reforming is considered the ideal generation method due to its high efficiency; however it ties with Electrolysis when the process by-product is taken into account. Photochemical Water Splitting stays at bottom due to its uncertainty in the improvement of its low production efficiency. EIOLCA comparison chart

Through EIOLCA on the three hydrogen generation methods, Steam Methane Reforming method produces large amount of Conventional Air Pollutant and Greenhouse gases in comparison to Electrolysis and Photochemical Water Splitting. This high pollution is mostly contributed from its production technique, high dependency on fossil fuel – methane, which is a high pollution process. As for toxic release, these three methods have shown similar value because toxic release is mostly caused by the construction stage of the generation plant and apparatus, instead of the production process, which is not different from one another. High energy for SMR is due to its delivery and transport of input energy, and its operation; since Electrolysis and Photochemical Water Splitting production materials are re-usable. Therefore, it is the production process operation itself that makes the difference between each generation methods, and the preparation work is not much different in terms of environmental impact. Electrolysis and Photochemical Water Splitting are a better generation method based on EIOLCA.

In Streamlined LCA, Photochemical Water Splitting ranked 1st in terms of its environmental impact, with an overall scoring of 78, higher than the 74 from Electrolysis, and the 41 from Steam Methane Reforming. Steam Methane Reforming scored only slightly more than half of Photochemical Water Splitting method was not surprising due to its production process ; although Steam Methane Reforming scored poorly in all sectors, its Material Choice and Gaseous Residue scored lowest due to the fact that its fossil fuel – methane based, and its large release of CO2. Primary and complementary process operation also scored relatively low because most of the pollutants are released during these two phases. Electrolysis scored very closely with Photochemical Water Splitting because their production technology is very similar, mainly relies on the splitting of water molecules; and materials used in process operation are both recyclable. However, since Photochemical Water Splitting uses solar energy as its main power to run the operation, it ended up with a final score slightly above Electrolysis.

Through Cost Analysis, annual operation cost (construction cost included) for each of the three hydrogen generation methods: Steam Methane Reforming, Electrolysis, and Photochemical Water Splitting were determined to be around US$ 60 million, US$ 65 million, and US$ 110 million. These values were calculated based on building and operating the hydrogen generation plant in Arizona, USA. With Steam Methane Reforming being the most economic, then electrolysis, and then Photochemical water splitting.

For societal impact, Steam Methane Reforming scored lower than the other two methods only because its high release of pollutants during its production process can be a potential threat to the plant workers' health.

According to this summarized scoring matrix, Steam Methane Reforming method provides highly efficient and economic production while making large amount of environmental damage; Electrolysis provides good but yet to improve efficiency and cost, and very little environmental impact; Photochemical Water Splitting provides poor production efficiency and expensive production cost, and very little environmental impact. Therefore, from the final scoring when making a balance between economic production and environmental impact, Electrolysis is the most suitable hydrogen generation method.

Steam Methane Reforming Process
Steam Methane Reforming (SMR) produces hydrogen in which a reactor with a catalyst is treated with steam promoting partial oxidations reactions and hydrogen production.

It consists of 3 stages:

1.Reformation of natural gas: Steam reacts with methane (CH4) at 750-800 oC to produce synthesis gas [1], which is a mixture of Carbon Monoxide (CO) and hydrogen (H2)

2.Shift reaction: Water gas shift (WGS) reaction is carried out; the steam reacts with the CO produced in first step over a catalyst to form carbon dioxide and hydrogen. Two stages are involved: High temperature shift (HTS) at 350 oC and Low temperature shift (LTS) at 190-210 oC [2].

3.Purification: Small quantities of improprieties such as carbon monoxide, carbon dioxide and hydrogen sulphide are included in the hydrogen produced, thus several purification procedures are required. The procedures are Feedstock purification – remove poisons, including chloride and sulphur. Product purification – CO2 is removed in a liquid absorption system. 99.99% pure product hydrogen is produced [1].

Electrolysis
Electrolysis is a chemical reaction that involves electricity as an energy source to pass through and break down a compound molecule in an aqueous solution. A power supply is connected to positive and negative electrodes which are called anode and cathode respectively. Electrode is a metal plate that conducts electricity and has contact with the electrolysed solution. The U-tube is then filled with water (H2O) to complete to circuit [3]. However, pure water does not conduct electricity. Salt (NaCl), function as an electrolyte, is added into water simply because it contains free ions that allows conduction of electricity [4].

Electrons release from the cathode and react with hydrogen ions and form hydrogen gas bubble at cathode. Similarly, oxygen ions release its electrons to anode and from oxygen gas bubble at anode. Both gaseous are collected in the tube. The reaction between water and the electrodes is not a single step equation. Instead, it includes a few reactions which are called Redox reaction [5].

Photocatalytic Water Splitting
Photocatalytic hydrogen production utilizes solar energy to produce hydrogen by splitting water molecules. In 1972, Japanese scientists Fujishima and Honda discovered that a photocatalyst such as titanium oxide can be used under ultraviolet (UV) light in order to produce hydrogen [6]. However, the process was extreme inefficient and could only utilize UV light which accounts for only 5% of total solar energy. Driven by increasing demand for renewable energy, the field of photochemical hydrogen production has seen rapid development in the past decade. Scientists have now developed processes that are capable of producing hydrogen using both UV and visible spectrum of light at efficiencies that are deemed acceptable in this field. Unlike conventional fossil fuel based methods, photochemical processes do not produce C02 as a byproduct. Therefore it has minimal affect on the environment. In addition, hydrogen produced through photochemical water splitting can be considered as a fully renewable source of energy due to its sole dependence on solar energy. However, the production rate and efficiency tends to be lower than other conventional methods.

Details on Economic Input-Output Life Cycle Analysis (EIOLCA)
Analysis was performed on [www.eiolca.net http://www.eiolca.net]

Steam Methane Reforming
Economic Input and Output Life Cycle Assessment is another approach to assess the environmental impact of hydrogen producing using Steam Methane reforming method. Natural gas is the primarily material for steam methane reforming, thus the natural gas distribution sector (#221200) is used as an EIOLCA model. The cost of natural gas required to produce hydrogen in a SMR plant is $18391711 (from cost analysis), thus this amount is entered in the EIOLCA for analysis.

Conventional Air Pollutants: The most significant air pollution is VOC (80.9%), which is due to the combustion sources in refinery. A high level of NOx is emitted in natural gas distribution as well, as it was produced during combustion. Power generation and supply and oil gas extraction shows a moderate level of SO2, CO, NOx, VOC and particulates emissions. These activities closely interact with the natural gas distribution as these are all processes in oil refinery. Cement is required to construct the infrastructure for the refinery wells; it is also needed in extraction process to prevent leakage in gas wells. It can be concluded that the mining and refinery process are the main factors of the emission of air pollutants.

Greenhouse Gases: Methane is one of the major components in natural gas. It is, the sole material that is needed for SMR. However, some methane leaks during the production and transportation process, which contributes most to the total methane emission. Pipeline transportation also gives a significant contribution to total greenhouse gas emission, as leakage occurs during transportation and the trucks emit some greenhouse gas as well.

Toxic Releases: Land releases and air releases are the two major toxic releases for natural gas distribution. Oil and gas extraction also contributes most to these releases. This is resulted from the contaminated solid residue during the mining process and the release of toxic chemical substances in the refinery process. Toxics are emitted during high temperature and the reaction between the chemical substances. Liquid residues are mostly water which is extracted from the natural gas and being disposed.

Energy: Pipeline transportation and natural gas distribution consume most energy (37% and 22.5% respectively), showing that the process is extremely energy intensive.

Electrolysis
The manufacturing stage of hydrogen is the main focus of how much environmental impact it does. In this case, electrolysis is the manufacturing process that was looked into. Using the data model in www.ieoica.net, electrolysis of hydrogen is under Other Basic Inorganic Chemical Manufacturing sector (#325180). The economic activity was raised to 62.4M USD which is the direct cost of the electrolysis plant.

SO2, CO and NOx are the major focus of the air pollutants because there are significant values of output for some sectors. Power generation and supply sector releases the most SO2 and NOX. This is because generating electricity requires combustion of fuel which forms Sulphur dioxide and Nitrogen monoxide. Another major release of SO2 comes from other basic inorganic chemical manufacturing sector. A lot of chemical reactions require heat to speed up the reaction rate and SO2 is formed from incomplete combustion of fuel. Truck transportation sector releases the most CO since incomplete combustion of fuel in automobile release large amount of carbon monoxide.

The most greenhouse gas emission is CO2. As mention previously in air pollutant emission analysis, producing inorganic chemicals and generating electricity require energy from combustion of fusel fuel, and this releases a large amount of CO2. Therefore, other basic inorganic chemical manufacturing and power generation and supply release the most CO2.

The majority of the toxic are Land releases which is formed mostly from Copper, nickel, lead and zinc mining. Metal mining creates tons of waste rocks and dust which counts as land releases. The percentage of land releases from mining is relatively large, about 77% of the total. The second majority, other basic inorganic chemical manufacturing, releases 9% of the total land releases.

The most significant air pollution is VOC (80.9%), which is due to the combustion sources in refinery. A high level of NOx is emitted in natural gas distribution as well, as it was produced during combustion. Power generation and supply and oil gas extraction shows a moderate level of SO2, CO, NOx, VOC and particulates emissions. These activities closely interact with the natural gas distribution as these are all processes in oil refinery. Cement is required to construct the infrastructure for the refinery wells; it is also needed in extraction process to prevent leakage in gas wells. From the above data, it can be concluded that the mining and refinery process are the main factors of the emission of air pollutants.

Photochemical Water Splitting
Photochemical hydrogen production is still in the research stage of development, thus it not possible to determine the exact cost of photochemical hydrogen production facility. Therefore Economic Input-Output Life Cycle Assessment (EIOLCA) was performed on a per million dollars of activity basis. The million dollars was divided amongst nine EIOLCA sectors, where Semiconductors and related device manufacturing and Scientific research and development services sectors contributed to 45% of the economic activity.

According to The EIOLCA results, the heavily coal based US power generation sector was responsible for the most SO2 and NOx releases. However, the truck transportation sector which is known for high tailpipe emissions released the most CO and VOCs. Steel production and Power generation sectors were tied for the top producer of greenhouse gases position with a GPW of 267 each as both of these processes release large amounts CO2 into to the atmosphere. Synthetic dye and pigment manufacturing sector which is responsible for the production of titanium oxide was another major contributor of greenhouse gases with 107 GWP. Ferroalloy and related product manufacturing sector was responsible the most non-point air, total air and water releases. However, primary nonferrous metal sector was the largest producer of point air toxic releases. Copper, nickel, lead and zinc mining sector produced highest land releases. Production of electronic equipment and air compressors units are probably responsible for the appearance of the last two sectors.

Steam Methane Reforming
The resource provisioning stage, primarily is the natural gas extraction, requires large amount of energy as well as many toxic substances are emitted in gaseous, liquid and solid form. Natural gas is as well not renewable. Besides, acid gases are emitted during oil refinery, which has adverse effects to the environment.

For process implementation stage, the analysis is towards the construction of the hydrogen generating plant. It is rather similar to other constructions and plant implementations, thus a low score of 9 is given in this process as constructions produces lots of wastes. However, there are some regulations such as Construction Dust Rules, which lowers the dust emission due to construction and hence improving the air quality near the plant.

In primary process operation, Carbon monoxide is produced in the first stage of SMR. CO is an odourless gas that is extremely toxic thus a score of zero is given for gas residue due to the degree of harmfulness of CO.

For complementary process operation, the main concern is the amount of emission of CO2. Mass of CO2 emitted is 2.51 times greater than that of hydrogen. CO2 is the major greenhouse gas, thus a low score is given for the process [8].

For Refurbishment, Recycling, Disposal, methanation is carried out to remove residues of carbon oxides, which is the major residues of the SMR. The demolishment of the plant contributes to all of solid, liquid and gaseous residue, thus low scores are given for these criteria.

Electrolysis
Resource Provisioning: Water is the major material in generating hydrogen. The supply of water is unlimited because there are a lot of major rivers in Arizona Besides adding salt into water, there is no further preparation of the water. The formation of salt requires solar energy to evaporate water and transportation of salt requires energy. The packaging of salt is the solid residue. They are made of plastic bag which are reusable. There are, liquid residues formed during evaporation of seawater. Steam is not toxic or radioactive Furthermore, evaporation of water happens all over the ocean.

Process Implementation: The extraction of the metal such as titanium is complex and required expensive metals to extract.Energy use for steel extraction is very high due to a large amount of heat energy is required to form steel. Installation of the equipment required large amount of energy since the equipment is relatively huge for mass production of hydrogen. In the extraction of titanium, there are many unwanted liquid and solid residues are formed in the process. Greenhouse gaseous such as NOx and SOx are also formed.

Primary Process Operation: Saltwater is electrolyzed and decomposed. It cannot be reused or recycled but it is not toxic or radioactive. A low voltage supply can activate the reaction of electrolysis. No energy is required when the manufacturing facility powers down. Oxygen gas is the by-product which is not a greenhouse gas or toxic.

Complementary Process Operation: Magnesium is used to form magnesium hydrides and store hydrogen in solid form. Magnesium can be recycled and reused to form hydride in the next cycle and this makes a close loop cycle.Energy used in packaging and transportation includes filling the hydrides into the tanks and loading the tanks on the trucks.

Refurbishment, Recycling, Disposal: All of the equipments that are made of steel and titanium are reusable and recyclable. The copper wires, glass tubes and tanks are also reusable; therefore it was assigned a perfect score.Energy used to refurbish and recycle steel is minimized

Photochemical Water Splitting
Resource Provisioning: The main resources for such a plant would only include water. Since water is abundant in nature a perfect score was given. A perfect score was also given to energy use as solar energy is abundant and the amount of energy used in a plant is insignificant compared to the total incident energy. Residues were given perfect scores as oxygen is the lone byproduct of the process.

Process Implementation: Primary materials required for a plant would include glass, titanium oxide, plastic, and steel, all of which are abundant in nature. A score of three was given to as these materials would probably be virgin. A score of zero was given to energy use as the production of glass as steel and mining of titanium oxide are all highly energy intensive processes. Solid residues was also given a zero as mining of titanium oxide and other raw material for production of steel and glass creates vast amounts of solid residues. A score of one was given to liquid and solid residues as glass production creates liquid residues while steel production produces NOx, SOx, and VOCs.

Process Operation: Material choice is given a perfect score since only water is consumed during the process. Energy use was also given perfect score as production is controlled through software. The primary process does not create any residues as oxygen; the only byproduct from the process is not considered as harmful emission. However, hydrogen cells require cleaning. Therefore a score of three was given to liquid residues while perfect scores were given to solid and gaseous residues.

Complementary Process Operation: Complementary process in a hydrogen plant is the storage of hydrogen. This process does not require material input, however it requires a large amount of energy. Therefore material choice was given a four while energy use only received a two. The compression process does not create any residues and a score of four was given to all residues accordingly.

Refurbishment, Recycling, Disposal: Material choice received perfect score of four as glass, plastic, and steel which accounts for most of the primary material needed in the process are recyclable. However, energy use was given a one as glass and steel components are high density material which requires a large amount of energy to transport. Solid residues was given a three as components such as titanium oxide films would not be recycled. There are no notable liquid or gaseous residues from hydrogen cells. Therefore a score of four was given.

Details on Cost Analysis
The cost is varied between each hydrogen plant. According to The Hydrogen Plant Challenge, the costs components vary for different plant size. For the scope of this project, a typical hydrogen plant size of 90 mmscfd is used as it is considered to have more environmental impact [13]. In addition, a reasonable assumption is made to estimate the costs of a hydrogen generation plant as stated in Hydrocarbon Engineering. An annual production of approximately 72000 tons, or 200 tons per day.

Steam Methane Reforming
The overall hydrogen production cost could be estimated over the life of the hydrogen plant, including the construction, operation and maintenance phase of the hydrogen plant. The major operating cost is the utility costs, including generation of export steam, power, fuel, boiler feed water and cooling water where fuel and feed contribute most to the utility costs. It is noticeable that the utility cost could be lowered if the refinery utility costs are favourable of steam production. Other costs such as capital cost, start up cost, operating costs (including replacement costs) and maintenance costs are also needed to be considered in the life cycle. Since the natural gas price fluctuates, it is impossible to obtain the actual natural gas price, so only an estimate is given.

The following is the summary of the direct costs based on calculations using Capital Recovery Factor= 0.054047 and Annualized cost = 0.41697 calculated from future costs for catalyst tube replacement at 10th and 20th year

Indirect costs:

Indirect costs are comprised of costs arising from hydrogen production by SMR such as pollution cost and healthcare cost. However, it is impossible to quantify the indirect costs caused by the operation of a hydrogen plant using SMR method. For instance, generation of hydrogen also produces large amount of Carbon dioxide, which adversely affects the environment, which add costs to the pollution and healthcare. Besides, the extraction of natural gas also contributes to pollution, which also adds costs. However, when hydrogen is produced, some industries such as automobiles may use hydrogen as an energy source and decrease the use of other source such as diesel or gas, and it reduces the pollution and consequently reduces the pollution and healthcare costs. As these costs is relatively hard to quantify and relatively small compared to the direct costs, so it is not included in the total costs.

Electrolysis
Direct cost: Direct cost of a hydrogen electrolysis plant includes construction cost, installation cost, equipment cost, labour cost, fuel cost and maintenance cost. The land cost and construction cost of the plant is estimated to be 35.6Million USD. The cost of major equipment is approximately 8.26M USD. Labour cost is 3.98M per year and fuel cost is 2M per year [16]. Assuming the maintenance cost is 2% of the plant cost per year, which is about 0.712M USD. The initial construction cost and equipment cost was converted into annual cost using Effective Interest Rate of 2.631% and Capital- Recovery Factor of 0.054047. The total direct cost per year is 62.4M USD.

Indirect cost: Indirect costs are classified as Health cost of the workers and Environmental cost such as release of greenhouse gaseous and toxic gaseous.

Photochemical Water Splitting
As previously mentioned a complete cost analysis of photochemical hydrogen production can not be performed as the technology has not been implemented to date. One can assume that the capital cost of a plant would be somewhat similar to the cost of a photovoltaic (PV) power plant. However, direct comparison can not be made as a unit of electricity is not comparable to a quantity of hydrogen.

In order to obtain a capital cost of the facility it is assumed PV electricity is used in an electrolysis process to produce hydrogen. With an approximate PV cost of $2.73 million per 1MV of electricity and 2.4MV per ton of hydrogen/day electrolysis energy efficiency, the capital cost of hydrogen is calculated to be $6.55 million per 1 ton of hydrogen per day. Therefore a plant producing 200 tons of hydrogen per day would cost approximately $1.3 billion. If an interest rate of 5% and plant life of 30 years is used, the equivalent annual cost is calculated to be $85 million [19].

The operating and maintenance cost of the plant can be calculated using similar assumptions. With an operating and maintenance cost of $46.16/KW/year for PV plants, the hydrogen plant mentioned above would cost $22 million per year. The cost of fuel for a photochemical hydrogen plant is negligible. Therefore total direct cost of the hydrogen plant is $107 million per year.

Photochemical hydrogen plant of this magnitude requires a large amount land. The loss of natural habitat and farm lands due to the construction of the plant could be considered as indirect costs. However, if the plant is constructed on a desert these costs can be minimized.

Details on Societal Analysis
All three hydrogen generation alternatives showed common societal impact when operating in residential or urban areas. Impacts includes aesthetic disapproval, concerns on hydrogen cell explosion, pollutant release from SMR and plant construction, and noises; which is likely to cause dispute between civilians with the local government and company if a plant is going to be build and operate. If these hydrogen generation plant were to be build in rural areas, Electrolysis and Photochemical Water Splitting would results very little societal impact; however, since SMR production process is not pollutant free, workers in the plant must be concerned about their health issues. Therefore, in terms of societal impact, Electrolysis and Photochemical Water Splitting are a better generation process.