HYDROGEN FROM ONLY SUSTAINABLE ENERGY
Energy Wasted Converting One Fuel to Another
In his 2003 State of the Union Address, President George W. Bush said, “Hydrogen can be produced from domestic sources – initially natural gas, eventually from coal. That’s important. If you can produce something yourself, it means you’re less dependent upon somebody else to produce it.”
There are significant losses whenever one form of energy is converted into another. In the past, the cheapest way of making hydrogen has been by reforming it from natural gas. This was because the gas was both plentiful and cheap. Most of the hydrogen produced today is made by this method. To split the hydrogen from the carbon in the natural gas (CH4), a process called steam reforming is used. The methane is mixed with high-temperature steam under pressure and, with a catalyst present, produces carbon monoxide (CO) and hydrogen. A second reaction, known as a shift reaction, is then applied to produce more hydrogen and some water from the CO. Partial oxidation can be used to transform other hydrocarbons into hydrogen. They are broken down into char, oils, and vapors by reacting them with limited amounts of oxygen to prevent complete combustion. The residues can then be steam reformed. About 40% of the energy in the gas is lost in the conversion process.
One of the problems with producing hydrogen from a fossil fuel is that there are always significant losses whenever one form of energy is converted into another. The energy-conversion efficiencies become less important, however, if the energy that is being used to produce hydrogen is from renewable sources. This is because the costs of the hydrogen will not be determined by the value of the feedstock, but by the amortization of the system’s costs per unit produced. The energy conversion efficiencies to produce hydrogen from wind or moving water should be roughly 20%. That would be infinitely better than much higher energy conversion-efficiencies for producing hydrogen from the non-renewable natural gas.
If we must import more LNG now to satisfy the growing demand for gas, obviously converting still more natural gas into hydrogen will only increase our nation’s dependence on the imported LNG. It would be bad enough to make hydrogen from the natural gas if the energy in that gas could be efficiently converted into hydrogen. The problem is, it cannot.
Hydrogen is not a fuel; it is an energy carrier, similar to a battery. The energy produced when hydrogen is used is simply that energy that was stored when it is freed from hydrogen-containing molecules, minus the losses. It is because of these losses that the depletable hydrocarbons should not be used as the feedstock for producing hydrogen, but used in their present forms.
Producing Hydrogen from Coal Increases Global Warming
Hydrogen can also be derived from coal-fired power plants, either by using the steam-reforming process or by electrolysis. Critics argue that if we use coal to produce the environmentally clean hydrogen, the global warming problem will actually be made much worse because of the increased CO2 emissions that would be produced by the centralized hydrogen plants. Producing hydrogen from coal produces more than twice as much carbon dioxide, per Btu, as does the burning of natural gas. The energy contained in the hydrogen that would be produced would be only a small fraction of the energy consumed to produce it.
The DOE is developing a process to produce hydrogen from coal using a combined-cycle steam reforming system that would capture heat to drive steam turbines that would produce electricity as a byproduct. Though this double use of the heat would increase the total efficiency to more acceptable levels, the mining and burning of the coal can cause serious environmental problems, including a substantial increase in the total CO2 being emitted into the atmosphere. These emissions not only would have been simply transferred from the vehicles to the centralized hydrogen producing plants, but they would be multiplied by all the coal that was consumed in the conversion process. The total emissions of greenhouse gases in grams per mile would be higher for hydrogen being produced from coal than from any other power system.
Carbon dioxide has not always been a problem. For the past 400,000 years, the concentrations of CO2 in the atmosphere have fluctuated between about 180 and 280 ppm (parts per million, the number of CO2 molecules per million molecules of air). But in the late 1800s, when humans started to burn fossil fuels in earnest, atmospheric CO2 began to increase with alarming speed, from about 280 ppm to the current level of almost 380 ppm, in a scant 100 years. Experts predict that CO2 could climb as high as 500 ppm by 2050 and possibly twice that by the end of this century. As the CO2 levels continue to rise, the planet will get hotter.
Most of the world’s industrialized nations
have already vowed to combat global warming by reining in their emissions of
carbon dioxide, the chief “greenhouse gas” blamed for trapping heat in the
earth’s atmosphere. But in March 2001
President George W. Bush had withdrawn
Of the carbon sequestering schemes being
proposed, one is being put into use. In
the southeastern corner of
Another idea that is being proposed is to sequester the carbon in stone. Serpentine or olivine, both magnesium-containing silicates, could be used as feedstock to fuel a chemical reaction that transforms the CO2 emissions into magnesium carbonate, a cousin of limestone. To initiate the reaction – known as “mineral carbonation” – the CO2 is compressed, heated, and mixed with the feedstock and a catalyst, such as sodium bicarbonate. To handle millions of tons of CO2 would require huge quantities of serpentine or olivine. A single mineral-carbonation plant would carve out a mountain and, of course, still more energy would be used to obtain these minerals and to supply the heat and energy to operate the process.
Other Environmental Problems from Coal
Under the rules proposed by the EPA, power plants that burn bituminous coal from the Midwestern and Eastern states would be forced to make steep cuts in their mercury emissions. The subbituminous Western coals being consumed by most Midwestern power plants because of their lower sulfur contents, have even higher mercury levels. Efforts to limit mercury from stack emissions have been prompted by a growing body of research showing the devastating effects that mercury can have on the brains and nervous system of fetuses and young children. Forty-four states have detected high levels of mercury in those freshwater fish that are high in the food chain.
In addition to those environmental problems caused by the combustion of coal, the mining of the coal can also cause serious water pollution. Drainage from underground mines, surface mines, and coal refuse piles is the oldest and most chronic industrial pollution problem in the Appalachian Coal Region. The pyrite in coal and overlaying strata, when exposed to air and water oxidizes, producing iron and sulfuric acid. The acid lowers the pH of the water, making it corrosive and unable to support many forms of aquatic life. Although the surface mining of the alkaline coals in our Western states can also cause water pollution, that pollution is normally not as serious as that produced by the mining of the acidic, Midwestern and Eastern bituminous coals. In addition to the aforementioned environmental problems, a large percentage of our nation’s coal reserves lie under the most productive farmlands of our Midwestern states. The ability of this rich farmland to produce food in the future would be seriously degraded by strip mining.
Acidification of Oceans Could Bring Greater Disaster than Global Warming
Another problem being caused by all human-generated carbon dioxide is that it is acidifying the oceans. Carbon dioxide (CO2) combines with water (H2O) to form carbonic acid (H2CO3). This weak acid – plus the acid rains produced by the nitrous oxides, ammonia, and sulfur dioxide – is increasing the acidity of the coastal waters. Researchers have seen in laboratory studies the effects of the lowering of the pH on almost every ocean creature that forms a calcium carbonate shell, including algae – the tiny creatures at the crucial bottom of the deepwater food chain – and coral, whose skeletons grow more slowing in water with a pH only slightly lower than normal. At least a third of the world’s fish species depend in part on coral reefs for their ecosystems.
Our Coal Reserves Are Also Finite and Will Also Peak
Some people believe that we can build giant plants to produce hydrogen, synthetic petroleum fuels and synthetic gas from our nations’ large coal reserves. Though it may be true that our coal reserves would last for several hundred years, that would only be if we were to maintain our present rate of consumption. If we were to produce liquid and gaseous fuels from coal, we would greatly accelerate the final depletion of that resource.
A paper entitled The Peak in U.S. Coal Production, by scientist Gregson
Vaux, presents an original study that indicates that coal would behave almost exactly
like Hubbert’s Peak Oil. The Department
of Energy’s EIA is predicting that
The following graphs are from Vaux’s paper.
The first graph shows the percentage of various energy sources used to run the
The above graph on the right shows
If we look at the next graph, it might seem that the Hubbert’s curve does not closely match the historic data. The fitted curve takes into account past production trends and predicts the peak date based on the assumption that once one half of the ultimate production has been reached, production will naturally decline as the remaining coal lies in thinner and deeper seams.
The EIA’s Annual
Energy Outlook 2004 was published before it was widely accepted that
The Vaux paper includes the following table
that summarizes the three EIA scenarios.
Huge Quantities of Coal Would be Consumed by Hydrogen Plants
Although the process of converting coal to hydrogen differs from that of converting coal to synthetic natural gas, many of the same chemical reactions are common to both. Pulverized coal is fed into a high-temperature reactor with steam and a deficiency of oxygen to prevent complete combustion. The gas produced is 40% hydrogen, 40% carbon monoxide, and about 15% CO2. Both processes require the use of a shift reaction to increase the hydrogen content and convert the CO to CO2. In both the coal-hydrogen and the coal-syngas plants, hydrogen is separated from the other impurities using the same PSA technology that has been used in refineries since the late 1970s. This process is based on the principal that absorbents are capable of adsorbing more impurities at higher partial gas pressures than lower. The impurities are adsorbed in a fixed-bed absorber at high gas pressure and then rejected as the system “swings” to a lower pressure. The hydrogen is not adsorbed. Running the gases through a series of these PSA “swing” reactions can completely adsorb the impurities to allow the production of hydrogen that is 99.9% pure. Though I have not seen any data concerning the quantities of water that would be consumed to produce the hydrogen from coal, I do know something about the coal-to-syngas process. Though there would be differences between the processes for producing hydrogen and syngas, the greatest variations in the coal and water requirements would be caused by the differences in the characteristics of the coals that might be used as feedstock. What follows is an analysis of the quantities of coal and water that would be used to produce the syngas. I believe the requirements for the hydrogen plants should be quite similar.
During the natural gas shortage of the early
1970s, laboratories in the
The coal gasification plants that were being proposed in 1973 were to be about twice the size of the Great Plains Coal Gasification Plant and would have produced about 250 million cubic feet of gas per day from about 16,000 tons of coal and between 7 million and 15 million gallons of water, depending mostly on the characteristics of the coal used. The coal consumed in just one day by just one of these proposed plants would have filled 228 seventy-ton hopper cars, a string of cars about 1½ mile long. The 16,000 tons of coal per day is equal to 11.1 tons per minute.
If just one of these giant coal gasification plants were to consume 16,000 tons of coal per day to produce 100 billion cubic feet a year, to produce a trillion cubic feet to fill the growing energy void produced by the falling gas production would require that 10 new plants be completed each year. The amount of coal required to supply those 10 plants would fill a string of hopper cars 5,478.75 miles long. If we were to produce enough syngas from these coal plants to replace all of the 20 Tcf of natural gas that is now being consumed, we would need 200 plants. Those 200 plants would require 1,168,800,000 tons of coal per year – enough coal to fill a string of hopper cars that would rap around the Earth’s equator 44 times.
Because the hydrogen would be used primarily to power vehicles and not to replace the gas that is used for primarily space-heating and industry, it is impossible to estimate the quantities of hydrogen that might be made from coal.
Huge Quantities of Carbon Dioxide Produced by Coal-Hydrogen Plants
Because the hydrogen content of coal is normally no more than 5%, when coal is used to produce either synthetic natural gas or hydrogen it is used primarily to supply the energy, and water is used as the chemical feedstock to supply the hydrogen. The amount of heat that is produced during the complete combustion of coal depends on the amounts of carbon, hydrogen, and oxygen that is in the coal and, to a lesser extent, on the sulfur content. The ratio of carbon to heat content depends on these heat-producing components, which can vary widely. Carbon is by far the major component of coal and the principal source of heat. The typical carbon contents for coal (dry basis) range from more than 60% for lignite to more than 80% for anthracite. Carbon combustion produces 14,600 Btu per pound. Although hydrogen generates about 62,000 Btu per pound, it accounts for only 5% or less of coal and not all of that is available for heat because some of it combines with oxygen to form water vapor. Also, the higher the oxygen content, the lower the coal’s heating value. This inverse relationship occurs because oxygen in the coal is bound to the carbon and has already partially oxidized that carbon, decreasing its ability to generate heat. The variations in the ratios of carbon to the heat content are due primarily to variations in the coal’s hydrogen content.
The typical carbon contents for coal (dry basis) range from more than 60% for lignite to more than 80% for anthracite. Carbon dioxide forms during the combustion of coal when one atom of carbon (C) unites with two atoms of oxygen (O2) from the air. Because the atomic weight of carbon is 12 and that of oxygen is 16, the atomic weight of the CO2 is 44. Based on that ratio and assuming complete combustion, one pound of carbon combines with 2.667 pounds of oxygen to produce 3.667 pounds of CO2. The carbon dioxide that would be produced from the complete combustion of one pound of lignite would be 2.2 pounds (3.667 x .60 = 2.20). The carbon dioxide produce from the combustion of one pound of anthracite would be 2.93 pounds (3.667 x 80 = 2.93), and the carbon dioxide that would be produced from a good grade of Eastern bituminous coal would be about 2.82 (2.336 x .77 = 2.82). Although the lignite will produce less CO2 per ton, because it contains less Btu per pound than the stronger Eastern coals, the CO2 emissions from burning it are normally greater.
If a coal-hydrogen plant consumed 16,000 tons of coal per day and that coal contained 70% carbon, that plant would emit 26,163 tons of carbon dioxide a day (16,000 x .70 x 2.336 = 26,163.2) or 9,556,036 tons of CO2 per year. At one atmosphere of pressure (14.7 psi) and at 32o Fahrenheit, carbon dioxide has a density of .12341 pounds per cubic foot. Dividing the 9,556,036 ton by the .12341 pounds equals the 154,866,473,543 cubic feet of CO2 that would be emitted per year. That would be equal to the volume of a cylinder having a diameter of one mile and a height of 1.34 miles.
(The volume of the gas at any given pressure is proportional to the temperature in degrees Kelvin. Zero degrees Kelvin is equal to -273.15 o Celsius, or -459.67 o Fahrenheit. At a temperature of 212o F (100 o C) the volume would be 36.6% greater than at 32 o F or 0 o C.)
Water Consumption Would be Even a Bigger Problem
Although the mining of all the coal to feed the hydrogen plants would involve tearing up our agricultural lands, the biggest problems could be caused by the huge amounts of water those hydrogen plants would consume. This water problem would not be limited to the semi-arid regions of the West that are already experiencing water shortages and dropping aquifers; it would apply to all the hydrogen plants not located near major lakes or rivers. A hydrogen plant that would consume 7 million gallons of water per day would consume at a rate of 4,872 gallons per minute. In a year, that plant would consume enough water to fill a tank having an area of one square mile and a depth of 12.27 feet. A plant consuming the 15 million gallons of water per day would consume 173.6 gallons per second and 10,416 gallons per minute. Each year the plant would consume enough water to fill a tank having that same one-square-mile area and a depth of 26.28 feet. Environmental disasters would be the inevitable result wherever the quantities of water taken exceeded the rates of replenishment.