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Hydrogen Economy Now 1

CAM ALLAM Cycle and Renewable-fuel base-load power-station

(An earlier version was posted elsewhere on Thursday, January 11, 2018 - 03:02 pm:)

Edward Chesky …Major (Retd) US Army USA

Mohideen Ibramsha 1968 Alumni of Thiagarajar College of Engineering, Madurai, TN, India 1974 intellectual son of PhD guide Prof. V.Rajaraman & Mrs. Dharma Rajaramn, CS, EE, IIT, Kanpur, UP, India 1991 First HOD of CSE, CEC [now BSAU] Chennai, TN, India Associate Professor (Retd), Computer Science, Framingham, MA, USA Consultant R&D, M A M College of Engineering, Trichy, TN, India Advisor, HyDIGIT Pte Ltd, Singapore Email: ibramsha7@yahoo.com

Introduction: This article is the first in a series of articles to follow on the topic of switching to a Hydrogen Economy as soon as possible.

ALLAM cycle uses supercritical CO2 as the working fluid. Flow designs are given for natural gas and synthetic natural gas input. Natural gas is a fossil fuel and synthetic natural gas is produced by gasification of coal which is a fossil fuel. When and how does mankind shift out of the fossil fuels and move to renewable sources like hydrogen? Synthetic natural gas could be produced from non-forest wood and thus replacing the coal gasification plant with non-forest wood gasification plant would move mankind from coal to renewable wood. The carbon in an old forest tree is similar to fossil fuel as the CO2 absorbed by an old tree would result in increasing the atmospheric CO2 concentration. We modify the ALLAM cycle to use hydrogen and name the cycle CAM ALLAM cycle corresponding to the first letters of ‘Chesky And Mohideen,’ the inventors being Chesky and Mohideen. We derive the CAM ALLAM cycle in stages from the ALLAM cycle. Analysis of ALLAM cycle: The system diagram of ALLAM cycle is given at. https://qzprod.files.wordpress.com/2017/11/allam-cycle1_colorcorrected.jpeg?quality=80&strip=all&w=940 . We describe the system diagram below.

An ‘Air Separation Unit’ supplies pure Oxygen to the ‘Combustor’ that receives natural gas and ‘circulating CO2.’ The output of the ‘Combustor’ drives the ‘CO2 Turbine’ which produces electric power and has an exhaust of CO2 and steam. The heat energy of the turbine exhaust is recovered by ‘Heat Exchanger’ and transferred to the ‘circulating CO2.’ The CO2 from the ‘Heat Exchanger’ after removing the water from the turbine exhaust is cooled and split into the ‘circulating CO2’ and CO2 for Carbon Capture and Storage. The CO2 that results from the burning of the natural gas alone is sent for CCS.

As we use hydrogen as fuel, there is no CO2 extraction. All the CO2 in the system is used as a working fluid. Thus the first step of conversion simply removes the CCS part of the ALLAM Cycle. The gas input is Hydrogen. We retain the air separation unit and burn the hydrogen with pure Oxygen to ensure that the input to the turbine is simply the super critical CO2 and the mixed steam. Removing the air separator would allow nitrogen also into the turbine. It might be possible to redesign the turbine for the changed input to the turbine. Such a redesign would take a few years for the new turbine to be introduced. To avoid the delay in abandoning fossil fuels, we sacrifice 10% of the power that is used by the air separator. From https://en.wikipedia.org/wiki/Allam_power_cycle we find that the combustor gets 4.75% oxygen, 1.25% CH4, and 94% supercritical CO2 as input. The output of the combustor is 2.75% of water and 97.25% of supercritical CO2. We expect that the above quantities correspond to full load. For ease of understanding, we state that the weight of the supercritical CO2 is 9,400 Kg. The actual weights could be different based on the power generated. We use a total of 10,000 Kg for ease of discussion. There seems to be some approximation in the above numbers. The methane burning equation is: CH4 + 2O2 ‘gives’ CO2 + 2H2O Including the molecular weights of the elements we get CH4 [(12 + 4) x 1 ] + 2 x O2 [ 2 x (16 x 2) ] ‘gives’ CO2 [ 12 + 2 x 16 ] + 2H2O [ 2 x ( 2 x 1 + 16) ] CH4 [ 16 ] + 2O2 [ 64 ] ‘gives’ CO2 [ 44 ] + 2H2O [ 36 ] The numbers given in the wikipedia article above for oxygen, methane, and resultant water and carbon dioxide are approximate. 600 Kg of oxygen and methane result in 600 x [ 44/80 ] Kg of supercritical CO2 and [ 36/80 ] x 600 Kg of water. We get 330 Kg of supercritical CO2 and 270 Kg of water. At full load, the turbine receives 9400 + 330 = 9730 Kg of supercritical CO2 and 270 Kg of water. At different loads, the turbine receives the following quantities.

For a total of 10,000 Kg at full load we get 9,730 Kg of supercritical CO2 and 270 Kg of steam. The supercritical CO2 decreases to 9,664 Kg; 9,598 Kg; 9,532 Kg; and 9,466 Kg for a load of 80%; 60%; 40%; and 20% respectively. The steam supplied to the turbine is 270 Kg at full load and reduces to 216 Kg; 162 Kg; 108 Kg; and 54 Kg for corresponding 80%; 60%; 40%; and 20% loads. We use hydrogen alone as fuel. Thus no CO2 is produced in the combustor. At full load we supplied 600 Kg of oxygen and methane. Out of this 600 Kg the weight of methane is 600 x [ 16 / 80 ] = 120 Kg. As the H2O is present as steam, we use LHV in our calculations. The heat given by methane [ CH4 ] is 50.00 MJ / Kg. Thus the total heat corresponding to full load is 120 x 50.00 MJ = 6,000 MJ. The hydrogen required to produce this LHV is 6,000 / 119.96 Kg, where 119.96 MJ/Kg is the LHV of one Kg of hydrogen. Thus the amount of hydrogen alone for full load is 50.02 Kg. The LHV values of methane and hydrogen are as given at https://en.wikipedia.org/wiki/Heat_of_combustion One Kg of hydrogen produces 9 Kg of water. Thus burning 50.02 Kg of hydrogen in the combustor would produce 450.18 Kg of water. However when we use CH4 as fuel only 270 Kg of water is produced in the combustor. To maintain just 270 Kg of water is produced inside the combustor, we need to reduce the amount of hydrogen burnt inside the combustor to 50.02 x [ 270/450.18 ] = 50.02 x 0.59976 = 30 Kg only. Ignoring the 0.02 Kg, we burn a total of 50 Kg of hydrogen, burning 30 Kg inside the combustor and 20 Kg outside the combustor. Thus, 60% of the required hydrogen is burnt inside the combustor and 40% of the hydrogen is burnt outside the combustor heating the supercritical CO2 through an additional heat exchanger. The hydrogen burnt in the additional heat exchanger is increased if necessary to overcome any efficiency of the heat exchanger being less than 100%. The amount of supercritical CO2 entering the turbine at full load is 9,730 Kg that reduces proportionately to 9,400 Kg as the load decreases. We need to extract 330 Kg of CO2 at no load and proportionately different amounts of CO2 at different loads. Thus we introduce a variable storage with maximum storage capacity of 330 Kg to extract the right amount of supercritical CO2 based on the load. After including the additional heat exchanger and the variable storage, we get the CAM ALLAM power cycle. The CAM ALLAM power cycle is fully renewable provided the hydrogen used is produced without any fossil fuel. Let us consider producing hydrogen using renewable only. We consider two aspects of solar power to indicate ramping up of hydrogen production using electrolysis.

When we replace CH4 by Hydrogen as fuel, the CAM ALLAM cycle has the following 7 components.

  1. Air Separator unit to supply pure Oxygen to the Combustor.

  2. The Combustor that receives pure Oxygen, all of the circulating supercritical CO2, and 60% of the Hydrogen fuel and produces the matching input to the turbine as the CH4 using ALLAM Cycle plant.

  3. The turbine used in the ALLAM Cycle

  4. The ‘Heat Exchanger’ used in the ALLAM Cycle

  5. The cooling plant used in the ALLAM Cycle

  6. Load based CO2 storage unit allowing the required load based CO2 only to be heated by the waste heat of the turbine exhaust as in the ALLAM Cycle and

  7. A Combustor cum heat exchanger in which the remaining 40% of the Hydrogen is burnt using air as the Combustor output does not enter the turbine. The heat energy from the 40% if Hydrogen is transferred to the CO2 heated by the ALLAM Cycle heat exchanger to transfer the energy to the CO2 that enters the turbine.

Thus for the CAM ALLAM Cycle we add just the last two components listed above and of course redesign the CH4 Combustors to burn Hydrogen. We consider Hydrogen production now. Hydrogen production: We want the hydrogen to be generated using renewable energy. Currently we have two technologies offering renewable energy: solar and wind. Both are intermittent. We concentrate on solar as – in our opinion – wind mills are vulnerable to hurricanes. The wind turbine needs to be mounted on tall towers which could fail due to the large bending moments on the tower during hurricane force winds. Solar has two technologies: thermal and photovoltaic. We consider the thermal version first. Solar Concentration: Normal belief on solar power says solar power station could not produce power when there is no sunlight. Technically this could be overcome by designing the solar plant to produce more power than required during the day and storing the excess energy for use when there is no sunlight. A solar concentration plant near Seville in Spain is generating power during the night also. From http://www.dailymail.co.uk/sciencetech/article-1393879/Gemasolar-Power-Plant-The-worlds-solar-power-station-generates-electricity-NIGHT.html?ITO=1490 we find that the plant stores energy in molten salt and that the stored energy could produce electricity for 15 hours in darkness. This facility allows this plant to produce electricity for 270 days without using any fossil fuel. The plant was designed for 15 hours of energy storage with 9 hours of sunshine. It is possible that larger power could not be developed because the control of heliostats beyond the current radius of the field was not possible or it was felt that producing 24 hours of electricity from just 9 hours of sunlight was enough. We believe augmentation of this plant to produce more power from 9 hours of sunshine would permit this plant to become a base-load power-station. A graph for the average monthly hours of sunshine at Seville, Spain is given at seville,Spain,https://weather-and-climate.com/average-monthly-hours-Sunshine,seville,Spain The graph was exported to the ‘Paint’ program and the pixel coordinates were read. For 400 hours the number of pixels was 161. The number of pixels for every month was read and the average sunshine in hours was calculated. The calculated values are given below.

  1. For January the daily average is 5.21 hours, with the monthly average of 161.49 hours.

  2. February with a monthly average of 163.98 hours has a daily average of 5.65 hours.

  3. A daily average of 6.97 hours of sunshine occurred in March with the monthly average being 216.15 hours.

  4. For April the daily average is 7.62 hours, with the monthly average of 228.57 hours.

  5. A daily average of 9.78 hours of sunshine occurred in May with the monthly average being 303.11 hours.

  6. June with a monthly average of 320.50 hours has a daily average of 10.68 hours.

  7. A daily average of 11.94 hours of sunshine occurred in July with the monthly average being 370.19 hours.

  8. August with a monthly average of 347.83 hours has a daily average of 11.22 hours.

  9. For September the daily average is 8.61 hours, with the monthly average of 258.39 hours.

  10. October with a monthly average of 211.18 hours has a daily average of 6.81 hours.

  11. For November the daily average is 5.47 hours, with the monthly average of 163.98 hours, and

  12. A daily average of 5.05 hours of sunshine occurred in December with the monthly average being 156.52 hours.

With 15 hours of storage in molten salt, any day with a minimum of 9 hours of sunshine receives 24 hours of electricity from the plant. By using more salt we could save more energy from the energy captured on days with more than 9 hours of sunshine. On an average 0.78 hours per day could be saved during May for a future day after August. In September this excess stored energy would be depleted at a rate of 0.39 hours daily. We compute the cumulative hours of storage assuming that the amount of salt is enough. May, June, July, and August have more than 9 hours of sunshine. In May, we save 0.78x31=24.18 hours of sunshine. In June we save 1.68x30=50.40 hours of sunshine. 2.94x31=91.14 hours of sunshine are saved in July and in August we save 2.22x31=68.82 hours of sunshine. In the four months the total saving is 24.18 + 50.40 + 91.14 + 68.82 = 234.54 hours of sunshine.

These 234.54 hours of saved energy would be consumed to meet the residual energy required to supply energy during the night. Since September has 8.61 hours of sunlight, the required 0.39 sunlight hours would be consumed from the cumulative storage.

We use 0.39x31=11.70 hours of stored energy in September. Likewise we use 2.19x31=67.89 and 3.53x30=105.90 hours of stored energy during October and November respectively. At the start of December we have 234.54 – 11.70 – 67.89 – 105.90 = 49.05 hours of stored sunshine. The average daily sunshine in December being 5.05 hours, we consume 3.95 hours of stored sunshine every night starting with December 1. The stored energy would come for 49.05/ 3.95 = 12.42 days. Thus starting with December 13 there is no supply of electricity after sunset until the 1st of next May.

The number of days of non-availability of renewable energy after sunset is 19 days in December, 31 days in January, 28 days in February, 31 days in March and 30 days in April a total of 139 days.

We have assumed that the average load after sunset is the same as during sunshine. During the nights the commercial load is zero. Let us assume that the average load after sunset is 0.9 times the average load during sunshine and recalculate the number of days of non-availability of renewable energy.

Then 15 hours of energy during sunlight rate would actually stretch to 15/0.9 = 16.67 hours without sunshine. Thus even during April there would be enough stored power once we have sunshine for 7.33 hours. Further for every hour of sunshine beyond 7.33 hours, we store 1.11 hours of energy required after sunset. We redo the calculations now in terms of hours of sunset.

During the first year of operation, no energy is stored during the months of January, February and March. However during April we get (7.62 – 7.33)/0.9 x 30 = 16.33 sunset hours of stored energy. Likewise we get (9.78 – 7.33)/0.9 x 31 = 84.39 hours in May, (10.68 – 7.33)/0.9 x 30 = 111.67 hours in June, (11.94 – 7.33)/0.9 * 31 = 158.79 hours in July, (11.22 – 7.33)/0.9 x 31 = 133.99 hours in August, and (8.61 – 7.33)/0.9 x 30 = 42.67 hours in September. At the end of September we have energy to supply 16.33 + 84.39 + 111.67 + 158.79 + 133.99 + 42.67 = 547.84 sunset hours.

In October, the average sunshine is 6.81 hours and thus we would use 17.91 hours of stored energy leaving 529.93 hours in storage at the end of October. During November we consume 62.00 hours and during December we consume 78.53 hours, leaving 389.40 sunset hours of energy in storage for the next year of operation.

Assuming that the average sunshine in the next year is the same as the current year, we would use (7.33 – 5.21) x 31/0.9 = 78.02 hours leaving (389.40 – 78.02) = 311.38 hours in storage. During February we consume (7.33 – 5.65) x 28/0.9 = 52.27 hours leaving (311.38 – 52.27) = 259.11 hours of sunset energy in storage. March consumes (7.33 – 6.97) x 31/0.9 = 12.40 hours. We find that at the end of March we have (259.11 – 12.40) = 246.71 hours of sunset energy. Thus there is no need for fossil fuel power if the load during sunset hours is 0.9 times the load during sunlight hours.

In the above discussion just reducing the load during sunset hours avoided fossil power. Alternately, we could augment the capacity of the plant to avoid fossil fuel. Instead of increasing the generation just to avoid using fossil fuel, we design the plant such that it generates enough power during the days of least sunshine. This design would generate more than the required power during the other days. Instead of just making electricity to avoid fossil fuels, we generate Hydrogen and Oxygen using the extra power. Accordingly, we accelerate the economy shift to Hydrogen even before 2050. The details of shifting most of the economy to hydrogen by 2050 could be seen at http://hydrogencouncil.com/wp-content/uploads/2017/11/Hydrogen-Scaling-up_Hydrogen-Council_2017.compressed.pdf We propose moving to the hydrogen economy earlier than 2050. We design solar power plants to meet the design load during days of least sunshine and use the excess power for electrolysis of water to generate Hydrogen and Oxygen. The energy used in an electrolysis cell would be a maximum when the anode and cathode are fully immersed in the water. By lifting the anode and the cathode the load generated by the electrolysis cell could be set at any level from full load to no load. Such variable load electrolysis cells convert all the excess power to Hydrogen and Oxygen. Solar roof: Instead of changing part of the roof to solar panels, we recommend making the full roof with solar panels and use the excess power to generate Hydrogen and Oxygen. Generation of Hydrogen and Oxygen after storing enough power for home consumption even during days of minimum sunshine eliminates the need for net metering. Every house becomes self sufficient and produces Hydrogen and Oxygen also. The Oxygen and Hydrogen so produced could be used in the CAM ALLAM cycle avoiding the air separator producing more power. Any excess Oxygen could as well be sold to fossil fuel plants employing CCS and CCU to increase their efficiency during the transition to full renewable energy. By building solar power based on the days of minimum sunshine, we hope we would reduce the greenhouse gases to pre-industrial levels soon, hopefully much earlier than 2050.

Once the greenhouse gases are reduced to pre-industrial levels, we could let the fossil fuels stay underground. Such retention of fossil fuels underground need not result in all the investment in fossil fuel plants being written off. We hope to consider different fossil fuel plants retaining most of the investment by simply replacing the fossil fuel with Hydrogen as fuel. For example, in a coal fired power plant the furnace could be replaced by a Combustor burning Hydrogen and the hot gases from the Combustor could be passed through the boiler to generate steam. Thus simply replacing the furnace retains the rest of the investment. We hope to consider this aspect after completing our analysis to establish the development of the Hydrogen Economy as soon as possible, hopefully now itself. Conclusion: The turbine used in the first ALLAM cycle plant produces 25 MW of power. This turbine is a reduced size version of the planned 295 MW turbine. http://news.toshiba.com/press-release/corporate/toshiba-supplies-first-kind-supercritical-co2-turbine-new-thermal-power-gene === The five companies have now completed major agreements to build a 25MW gross electric (50MWt) demonstration plant in Texas. Through the successful completion of operating tests, the demonstration plant is intended to provide the basis for the construction of the first 295MWe full-scale commercial plant. ===

With a 25 MW power plant, with an average of 5 KW per home, 5,000 homes could be covered. Such coverage could be done by a distribution network local to a town. If the plant develops 300 MW then the distribution would cover 60,000 homes across more than one town. Such a network would have long transmission lines. With the storms dumping ice and not snow alone, long distance transmission lines are vulnerable. As the 25 MW turbine is already delivered and is expected to work as planned during the ‘First Fire’ possibly during the first quarter of 2018, we hope more plants of 25 MW capacity get built offering hurricane-proof power. On December 30, 2017 we found a depressing fact. http://www.wired.co.uk/article/toyota-mirai-hydrogen-car-replicate-prius-success === The vast majority of hydrogen is generated using fossil fuels, which simply shifts C02 generation from tailpipe to production facility. === We hope our strategy explained above of excess solar power would eliminate use of fossil fuels for Hydrogen production soon.

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