Photovoltaic Nitrogen-fixation and organic farming literature review: Difference between revisions

Revision as of 21:48, 3 May 2016

This literature review supported the following publication:

Z. Du, D. Denkenberger, J.M. Pearce, Solar photovoltaic powered on-site ammonia production for nitrogen fertilization, Solar Energy, 122, 562-568 (2015). http://dx.doi.org/10.1016/j.solener.2015.09.035 open access

Ammonia synthesis is the most important step for nitrogen-fertilizer production and consumes approximately 1% of the world’s energy production and energy-related greenhouse gas emissions. In addition to the concomitant emissions caused by ammonia and nitrogen fertilizer synthesis, centrally produced fertilizer that must be distributed to farms also harms the environment because of the embodied energy of transportation. An environmentally-optimal nitrogen fertilizer system would be distributed on farms themselves using only renewable inputs. Recent developments in solar photovoltaic technology and subsystems for ammonia production have made non-organic on-site ammonia production physically possible. This study provides a technical evaluation of the process for on-site nitrogen-fertilization of corn using solar photovoltaic electricity as the energy input. The system consists of a water electrolysis system to generate hydrogen and a membrane system to generate nitrogen needed as material inputs. Total power consumption for syngas preparation to generate a unit of ammonia is calculated. System total energy consumption is calculated while compensating syngas preparation with heat recovery. Five case-study locations are evaluated to determine their suggested nitrogen fertilizer addition (N-rate) for corn growth and the energy consumption for suggested N-rate is calculated. The System Advisor Model (SAM) is then used to simulate the PV system output for those five locations. Finally, the PV land use required as a fraction of the corn field area is determined. The results indicate that because PV is so much more efficient at solar energy conversion than organic methods, even the worst case evaluated in Indiana requires less than 1% of the corn field converted to a PV system to provide enough energy to generate sufficient amounts of ammonia for fertilizer for the remaining corn. The system was modeled to provide ammonia to fertilize for corn fields larger than 1079 acres with the worst soil conditions, the area of which applies to more than half of cropland in the U.S. in 2011. As the finiteness and emissions of fossil fuel production of nitrogen become more important, this renewable system should become economical and future investigations into its overall viability are warranted.

See: Solar Photovoltaic Powered On-Site Ammonia Production for Nitrogen Fertilization

Nitrogen Management for corn

Nitrogen Management on U.S. Corn Acres, 2001-10

Three criteria for good N management
1. Rate: no more N than 40% more than that removed with crop at harvest.(How second term be determined?)
2. Timing: no N for crop planted in spring (All corns are planted in spring?)
3. Method: inject or incorporate instead of broadcasting in soil surface.(~~What are typical inject or incorporation method?~~ Applying with irrigation water.)
Trends
1. 97% planted corns received N, increased 18% percent from 2001 to 2010.
2. From 2001 to 2010, national did-not-meet-rate decrease from 41% to 31%. However, timing and method did not improve. Did-not-meet-timing increase from 32% to 35%; did-not-meet-method remained 38%.
3. N price double from 2000 to 2008, then drop from 2008 to 2010(~~Why?~~ Production of N is energy intensive process, thus N price relied greatly on fuel price.).
4. Corn receiving commercial N fertilizer dropped from 84% to 82% while receiving manure increased from 16% to 18%.
5. Farmer with manure as N source has no improvement(92%) in N-management. This may due to:
  1. Manure is used as a substitute for commercial fertilizer, due to increase price from 2001 to 2008;
  2. Manure is more difficult to manage.
Comment:
1. ~~Why rate criteria leave such huge margin(40%)?~~ Some suggested N rates themselves have great range like from 450-2000 lbs/ac, depending on complex soil conditions.

Nitrogen Management Guidelines for Corn in Indiana

Agronomic Optimum N Rate = AONR, defines N rate produces maximum grain yield, regardless of cost. It may vary greatly in different years. (For West Lafayette, it ranged from 130-221 lbs N/ac)
Economic Optimum N Rates = EONR, defines N rate result in maximum economic input-output ratio. EONR influenced greatly by N cost and grain price.
Traditional rule of thumb is driven by yield. For corn or soybean, N/yield rate is 1 lb/bushel; if corn follows corn/wheat, N/yield rate = 1.2 lb/bushel
N/yield rate is not linear, meaning in the end, more N will not result in more yield. More N only jeopardize environment.
New method for N rate recommendations are based on data, linking yield response to N with grain price and N cost.
Trial method:ranged N: 0(except for starter N) to 286 lbs/ac; UAN; 74% rotated corn, 26% continuous corn; regional and soil differences are considered in AONR; irrigated sandy soil guideline is not provided due to lack of field;
Table of AONR for corn following soybean in non-irrigated sandy soil in different regions of Indiana is given in Fig. 2.
Tables of EONR for corn following soybean in different regions of Indiana is given in Table 1, Table 2 and Table 3.
Guideline for continuous corn is not given.

Comments: Neither method of determining AONR nor EONR is given. So these data can only be used in Indiana.

Fertilizing Corn

Content
1. Manure problems: potential weed; soluble salt; excessive nutrient levels, N-leaching to ground water; high P.
2. Different levels of soil samples are needed annually to determined available N. Detailed steps for acquiring soil samples are described. N03, extractable P,K,Zn and Fe and soil PH, soil organic matter, and soluble salts can be determined.
3. Suggested N(lb/ac) for irrigated and dry land are separately given in Table 2 and Table 3. The suggestion has been adjusted according to soil N level and organic matter percentage. Be aware, following N still need be subtracted from suggested N from Table 2/3 to get the actual suggested usage of N.
  1. N from manure and previous legume crops; N credit in some common manure and left by previous legume crops are given in Table 1.
  2. N in irrigation water. 2.7 lbs of N per ppm of NO3 in irrigation water. should be subtracted for each ac-foot.
4. Based on expected yield (bu/ac), equation of suggested N for irrigated land is given. This equation has taken subtraction of N into consideration. (To see detailed calculation given by University of Nebraska, refer to Fertilizer Suggestion for Corn, this literature is reviewed below)
5. Method and timing
  1. For best efficiency, start fertilizing 30-40 days after planting (or plants have six leaves).
  2. All fertilizer should be applied before tasseling.
  3. Fall fertilizing NOT suggested.
  4. Apply N with irrigation water can improve N use efficiency.
  5. Timely monitoring the nutrient in plants and adjust N application accordingly is recommended.
6. P, K, Zn, S, Fe and other nutrient are also suggested in this article.
Comment: This suggestion is based on expected yield. Author suggested some nutrient is critic for corn in Colorado, but not suggest whether this N suggestion is for Colorado only or universal?

Fertilizer Suggestion for Corn

Fertilizer Suggestions for Corn

Suggested nitrogen is given by calculation. This suggestion is driven by yield. Two equations are given, one for suggested N for desired grain forage, the other for desired silage. Factors of these equations include:
1. Nitrate-N ppm in soil
  This weighted average ppm depends on both ppm of each layer and thickness of each layer. Example of calculation of weighted average ppm is shown in Table IV.
2. Organic matter percentage in soil
3. N from legume, manure and irrigation water
  Estimated nitrogen credit from some common crops are given in Table V, for both fine textured soil and sandy soils.
4. Price adjustment
  This factor is influenced by both N and corn price, suggested number is given in Table II.
5. Timing adjustment
  With spring preplant application as reference, split, mostly pre-plant and mostly fall timing factors are given in Table III.
Comment
1. Coefficient for those factors mentioned above is not clear whether based on regional study (like in Nebraska) or nationwide.
2. Timeline for timing factor is not clearly defined.

Cornstalk Testing to Evaluate the Nitrogen Status of Mature Corn: Nitrogen Management Assurance

N status of corn (what status?) can be determined by measuring N concentration in lower portion of corn stalk at the end of growing season.
1. Method can be used to determined whether exceeded yield corns have been treated with over dosed N. (~~Why this is necessary?~~ Upon corn being mature, N in cornstalk move to ear. N concentration will drop. However, if N is used over dose, N will accumulate in cornstalk. Thus, this method can help distinguish overdose to sufficiency)
2. Two phase relationship between nitrate concentration in stalk and N availability in root zone.
  1. First step: nitrate concentration in stalk remains constant while N in root zone increase. (Not absorbing or transport N to other zone?)
  2. Second step:nitrate concentration increase with N in root zone. (All accumulate in stalk or partial?)
  3. Experiment is analyzed that while stalks are tested to have more than 450 ppm, they all have maximum yield. However, it is also stated that under 2000 ppm, decrease of yield is found in relative field. Also, Figure 3 is not persuasive, because it shows 2000 ppm in stalk has significant excess for maximum yield. ~~450 ppm is in season data, at harvest, optimum result turn out to be 2000 ppm. Thus, the optimum region is given by 450-2000 ppm nitrate-N in stalk.~~(Or some corn requires only 450 ppm in stalk to reach maximum, while some requires more than this ppm; but above 3000, there is no additional yield due to more ppm. Meaning 450 has best fertilizer efficiency, while 3000 has worst)
  4. While above 3000 ppm nitrate-N is observed in stalk, no more yield is observed with more fertilizer.
  5. While N deficiency is observed, more fertilizer will not improve situation.(Deficiency is due to plants' own defects?)
Rainfall may lead to N loss.

Pre-sidedress Nitrate Test

In season test, used to determine nitrate-N in soil.(Is it true nitrate-N is by product by manure and last year's forage legume crops? What is the form of fertilizer nitrogen?)
Measuring time should before sidedress.(According to UI extension, sidedress is suggested to be prior to 6-8 leaves stage.)
Scenario the need PSNT:
1. 2nd year following sod (What kinds of sod? What about legume?)
2. Not enough manure was applied to meet expected N needs.(Is it absolutely necessary to use manure?)
Scenario should not use PSNT
In this part, several scenarios are suggested in which PSTN might be inaccurate. However, according to slides from UMD, several different scenarios are listed. What is the principle for not using PSNT?
Interpretation of PSNT results are given in Table 1. (Is this for New York States Only or nationwide?)

Managing Nitrogen

This handbook is based on Illinois' situation, but most knowledge can be applied universally.
1 bushel contains 0.8 lbs nitrogen; 2/3 N is in grains. Thus, 200 bushel corn removes 240 lbs N in soil before harvest. So, 1 bushel requires 1.2 lbs N.
1. For economic adjustment, this rate may drop down along corn/N price
2. ~~Yield of corns following soybeans has little relation with N rate? Or just has dropped N rate?~~
  1. Soybeans provides vary amount of N, which leads to uncertainty of nitrate-N in soil.
  2. Hybrids may be good at both extracting N from soil and using them.
A different method has been shown and discussed to measure N rate for corn following corn and corn following soybean.
1. Use average data to draw curve to illustrate N-rate and yield relation. This method can only be used in single trials, can not be used to average different trials.
2. Use the curve drawn from a single trial, after subtract yield at 0 N-rate, according to N and corn price, it can be shown so called 'return to N'(RTN).
3. Average RTN based on different 40 trials are shown in Figure 9.5. However, compare to Figure 9.4, its maximum RTN (MRTN) is only half of the one shown in Figure 9.4. The reason is not explained. If it's due to some low RTN, then the average RTN from different trials will have little useful sense for any single trial!
Yield based N is suggested to be not recommended.
1. Paper claims there is no guarantee of N rate to no deficiency of N, because flat tail of N rate and yield tail. However, there are some minimum N rate under which decrease of yield will appear.
Factors that affect nitrogen availability
1. Immobilization: N from inorganic(ammonium NH4+ and nitrate NO3-) to organic form.
  Microbe need carbon (What kind of residue?) as well as N. For growth, C:N ratio is around 8:1 to 12:1. For consumption, C:N ratio is 20:1. If soil environment has higher ratio than this (such as cornstalk, which has C:N 50:1 to 60:1), microbes will need additional N. If soil environment has C:N ratio less than 20:1 (Such as soybean residues), microbes will release excessive N (Is these N immobilized?)(Will microbes directly immobilize ammonia and nitrate, or there must be organics?)
2. Mineralization: N from organic to NH4+.
  Since organic N is tied to organic matters, it needs to be mineralized to NH4+ for crops to absorb. NH4+ is released during decomposition of organic matters by microorganisms, or from dead microorganisms.
3. Nitrification Process of NHH4+ turns into NO2- then finally turns into NO3-.
  1. Following conditions will accelerate: Temperature 60 to 85 F, PH slightly acid t slightly basic, good soil aeration.
  2. NO2- is toxic. While soil is very acid or if N03- is saturated, bacteria is actively to produce NO3-. This happens usually when manure is injected to poorly drained soils.
  3. NH4+ cannot be lost through leaching; NO2- and NO3- can, so it's good to delay nitrification until crops start to take N. Corn usually take NH4+ and NO3- in ratio of 1:4.
4. Denitrification, NO2-, NO3- is transferred to N2O by anaerobic bacteria, causing N lost in some non-sandy land. This could be a significant N lost while land N is saturated and temperature is suitable.
5. Leaching. Rainfall in loamy land will drain out N into flow path directly if precipitation is large enough (6 inch). For finer soils, same precipitation will not drain N that deep, and before next rainfall, suction force will drag N back to normal level.
N test
Since N in soil is less likely to be denitrified, N test around uptaking time of crops is more reasonable.
1. Total soil nitrogen test. Test total available N according to organic matter. This tend to be inaccurate due to complexity of de/nitrification.
2. Illinois soil nitrogen test
3. Early spring nitrate-N test.
  May be greatly influence by rainfall condition each year. (In lomay land? Or in fine land also?)
4. Pre-Sidedressing Nitrogen Test (PSNT).
  1. More accurate for high yield lands have received manure or legume crops. (Is it because this eliminate situation for low yield that may due to whether condition that will lead to inaccuracy of ESNT shown above?)
  2. Only useful for crops are about to receive sidedress.
  3. Only accurate with small startr. Sidedress might be delayed by rainfall. (Some say fertilizing in rainfall is not harmful at all?)
  4. PSNT depends greatly on measurement's accuracy.
Plant's N test (Also refer to cornstalk testing)
1. plant tissue testing
2. SPAD meter. Determine N status according to how much light passes leaves. (Does this reading affected by plant species?)
3. Crop color sensing tech. Remote optical sensing or mounted on applicators to measure relative greenness of crop canopy.
Fertilizer
1. Anhydrous ammonia (NH3).
  1. Least expensive, highest N percentage by weight.
  2. Liquid under pressure
  3. Dangerous in gas phase in air. Stores under high pressure (200 lbs/inch^2)
  4. Uniformity is affected by hose length, air temperature etc.. Several methods and tools can be applied to reduce these affect.
  5. Anhydrous ammonia will kill desirable microorganisms in the topsoil. But for long term concern, it's considered to be a enhancement for microbes.
2. Ammonium nitrate (NH4NO3) 34% N (34-0-0, N-P-K?)
  1. 50% of AN is NO3-, which tends to both leaching and denitrification.
  2. Not easily volatilized, so can be used in surface.
  3. Can be used as explosives, so not recommended.
3. Urea (CO[NH2]2), (46-0-0)
  1. Soluble, move freely up down with soil water.
  2. Change into NH3, then NH4. Conversion is favored by temperature. While conversion at surface, NH4 may be lost. Following condition will help loss.
    1. Temperature higher than 55F
    2. Urea not incorporated
    3. Crops residue remains on soil surface.
    4. Application rate greater than 100 lbs/ac
    5. Rapid drying moist soil
    6. Low cation exchange of soil
    7. Soil are neutral or alkaline in reaction
4. Ammonium sulfate ([NH4]2SO4), 21% N.
  1. Not volatile, good for surface application
  2. If in dry soils, AS might not be able to reach root zone, as well as some other kinds of ammonia based fertilizer.
  3. While applying for deficiency of N, this might lead to over use of sulfur. But this should not be a concern, since S moves out quick and cause no environment issue.
  4. Acid material, need lime to neutralize timely. (Will lime cause harmful issues?)
5. Nitrogen solutions. Most common is urea-containing-solutions (UAN, urea ammonia nitrate). These fertilizers have combined properties of those mentioned above, should be applied according to combination of composition.
6. Ammoniated phosphate, mostly used as phosphorus fertilizer.
7. Organic-N fertilizers. Manure, poultry litter etc.
  1. For environmental concern, should be apply far from water body and steep slopes.
  2. Limited by phosphorous content.
Nitrogen Fertilizer Amendments
Product to make N used more efficiently
1. Nitrification inhibitors. Since NO3- is easy to either denitrify or leach, inhibitors like dicyandiamide can significantly maintain N in NH4+ form. (But corns as an absorption ratio of NH4+:NO3- of 1:4, means most of the N should be in NO3- form to be absorbed, N being inhibited for too long might not be good.)
  1. Use while soil condition is conductive to leaching or denitrification.
  2. Used in autumn to avoid N loss for following, effect might vary greatly by soil condition.
  3. Not recommended for sidedressing.
  4. Used while N is applied below optimum rate.
2. Urease inhibitors
  Added to UAN solution or urea to reduce the potential of volatilization while surface applied.
  1. Good benefit while temperature is above 50F while surface applied.
  2. Good while residue content is high
  3. Ineffective while incorporated or tillaged.
3. Coatings and ureaform
  Method that prevent urea from deforming to ~~NH4+, which is highly volatile~~ NH4+ is not volatile, because its charge, NH3 is volatile, but NH4+ can easily transfer to NH3.
Timing
1. Fall applications
  1. Only be done at soil has low loss potential. (Not poorly drained nor too well drained, etc)
  2. Fall app are more likely an economical concern
  3. Only applicable while bare soil is below 50F. Refer to soil temperature map.
2. Winter application
  Winter app of urea in the surface has great loss potential for corn. (But might be effective for wheat.)
3. Spring application (preplant)
  1. Prevents plants damage.
  2. Planting should have higher timing priority than fertilizing.
  3. While applying anhydrous ammonia after planting, make application away from seeds' row to prevent seed injury.
4. Sidedress
  1. Minimized N loss due to close to the time of crop uptake.
  2. PSNT help farmer determined whether full rate is necessary.
  3. Anhydrous ammonia is preferred.
  4. Might be affected by rain season (Both before or after applying)
  5. Corn may suffer root damage
  6. Susceptible to midseason loss
  7. Refer to Pre-Sidedressing Nitrogen Test
Methods
1. Subsurface application
  1. All low pressure ammonia solution should be injected into soil. Depth may vary with ammonia content.
  2. In very coarse soil, ammonia may move upward and lost in gas form.
  3. Moist is key to detain ammonia if tillage. Deep tillage should wait until ammonia is transferred to NH4+
  4. Free ammonia is harmful, avoid direct contact with seeds.
  5. Although UAN is capable to surface app, but it's better for subsurface app
  6. While use urea in subsurface app, avoid contact with seeds.
2. Surface application
  1. Residue in surface has urease, which may lead to low yield if UAN is applied in surface.
  2. Dribble of UAN can reduce N loss.
  3. Aerial app can be used as contingency while other methods are not applicable. Don't use aerial app for growing corn, since it may damage leaves.
Nitrogen rates for other crops are introduced

Rotation Effect

Typical legume includes: alfalfa, clover, peas, beans, soybeans, peanuts.

The Corn and Soybean Rotation Effect

The Corn and Soybean Rotation Effect
Yield increase associated with crop rotation is called rotation effect. This research is based on Minnesota and Wisconsin cases studies.

Corn yield
1. First year corn was observed with 15% or greater yield higher than continuous corn. (~~How to define first year corn? What's the land use before corn?~~ Corn after hay is called first year corn. Refer to Nitrogen Needs of 1st Year Corn)
2. Immediate from 2nd year, advantage of yield is not significant. This means except for annual rotation, other rotation will not significantly help yield!
3. Corn annually rotated with soybean was observed with 13% or greater yield higher than continuous corn.
4. With yield increasing of continuous corn, advantage of first year/rotation declines, however, advantage still remained. (What's the reason?)
5. Positive effect by environment was observed to both annually and first year corn.
6. Rotation has little response with environment change.
7. Both positive and negative environment condition for corns are listed.
Soybean
1. From third year, there had been no significant yield advantage of rotation against continuous soybean.
2. First year soybeans are susceptible to positive environment affect. Rotation soybean are not susceptible to neither positive nor negative environmental affect.
3. Both positive and negative environment condition for soybeans are listed.
Both maximum yield of corns and soybeans appeared at 1st year, not annual rotation. The reason for this is not discussed!

Nitrogen Needs of 1st Year Corn

N available for corn in following years after legume are given in Table 1. This amount depends on percentage of legume in a field. (How to quantify?)
To prevent N loss in winter, turn over legume only when soil temperature drops below 45F.
Starter N could have small contribute for 1st year corn yield. (Up to 10%), However, significant amount of sidedress N did not show correspondent yield increase.
When used as forage, sidedress N slightly increase crude and soluble protein content in corn, but this did not affect the milk production. Thus, 1st sidedressing is absolutely unnecessary. So is PSNT.

Crop Rotations and Conservation Tillage

Effects of rotation
1. Reduce fertilizer usage.
2. Rotation help control crop-disease problem. (How?)
3. Enhance soil physical properties
4. Control P, K in soil.
5. Help some time sensitive plants such as corn to get better time managements.
6. Rotation might need additional tools, human resources than continuous crops.
Using crop rotations for conservation tillage
1. Problem caused by no-till corn fields can be relieved by hay-corn rotation
  1. Perennial weeds;Leaf diseases;Insect problems can be relieved
  2. Heavy residue left by corn will result in cooler soil temperature, which might lead to yield decrease. Hay residue can help increase soil structure.
2. Three year corn-soybean rotation has similar effect, but it may not control overwinter erosion, hard soil in spring and insect problems.

Conservation Tillage

Conservation Tillage
Method that leaves previous crop residue before or after next planting. This helps reduce soil erosion and runoff.

Methods
1. No-till. Plant crops directly into residue that has not been tilled at all.
2. Strip-till. Only till narrow strip before planting
3. Ridge-till. Residues are cleared off ridge into furrows to make way for planting
4. Mulch-till. Other method leaves one third of soil covered with residue.
Benefits
1. Environmental
  1. reduce soil erosion by as much as 60%-90%, depending on methods.
  2. Improve soil and water quality by adding more organic matter. (Why adding organic matter helps these?)
  3. Reduce water loss. Optimize soil moisture

Crop rotation and corn and soybean yield

Method: corn-corn-soybean, one third soybean each year.
Result:
1. Both Soy-corn rotation and 1st year CCS have similar maximum yield.
2. 2nd year CCS was not observed significant yield advantage against continuous corn.
3. Soybean follow continuous years of corn(in this case two years) has better yield than corn-soy rotation. (But in this article, it shows a CSS column, should it be a typo?)

Ammonia Synthesis

Low Energy Consumption Ammonia Production

No obvious trend since 1900, consumption ranging between 6.7 and 7.4 Gcal/t NH3 ('1 Gcal = 1.6222~ MWatt hours')
Modern ammonia plants have energy efficiency around 64%

Catalytic Synthesis of Ammonia-A 'Never-Ending Story'?

Industrial process efficiency can reach 4.81Gcal/t NH3. (4.81*10^9 Cal per Ton?)
1. Biggest energy loss is in methane reforming. Lost 1.18 Gcal/t
2. Slight energy loss in ammonia synthesis (0.37 Gcal/t)
3. What are the rest energy loss?
4. Achieved with iron catalyst or ruthenium-based catalyst.
5. Catalyst improvement could increase efficiency.
6. Reduction of base compound pressure could reduce process price.
7. Main synthesis method has already been optimized, should not be adjust by new methods.
8. Hydrogen is made from methane, and need to be purified.
Under industrial conditions (What conditions?), nitrogen coverage is low. (What's nitrogen coverage?)
Principle of Iron and ruthenium catalysts are discussed.

Developing more sustainable processes for ammonia synthesis

Conventional Haber-Bosch process works under 200-500 atm, 500-600C, by catalyst of Fe3O4/K2O/Al2O3.
1. Produce 160 million metric tons of ammonia per year.
2. Consume world's 1%-2% energy supply.
3. Generate 300 million tons of CO2
Biological nitrogen fixation can be a model to produce ammonia under ambient conditions.
1. Among all studied metal-dinitrogens, only molybdenum-dinitrogen has been observed to catalyze conversion under ambient condition.
Other complexes are discussed.

Ammonia Synthesis at Atmospheric Pressure

Traditional Haber-Bosch process
1. In HB process, gas decrease whiile process goes on, thus, high pressure is required to push reaction toward right.
2. At 430C-480C, HB process equilibrium conversion is around 10%-15%.
Solid state proton H+ conductors can be used to realize low pressure process.
1. H+ conductors can operate at temperatures in which industrial hydro- an dehydrogenation reaction take place. (What temperature?)
2. Ammonia and methanol production are equilibrium limited at operation conditions. (What does this mean?)
Process flow:
1. Gaseous H2 pass through quartz (Why?) tube over anode of the proton-conducting cell-reactor.(Waht's the voltage?), H2 are transferred to H+.
2. H+ will be transported to cathode, where they react with N2 (Transported through ceramic tube, diluted by helium) to form NH3. NH3 and left N2 are then move out.
NH3 rate
1. Conversion is related to I/2F, where I is imposed current, F is Faraday's constant(?).
2. At SSD temperature 570C, 1.8% N2 in He pass through cathode at rate of 8.3*10^-8 m^3/s, H2 flow at 5.0*1o^-y m^3/s. Both NH3 conversion rate and H2 conversion rate are shown in Fig 2.
3. (How to read this Fig?)

Ammonia synthesis at low temperatures

High temperature in traditional ammonia synthesis is to deal both H- and N- metal bond in their surface.
High temperature shift N2 H2 synthesis toward left, while high pressure shit N2 H2 synthesis toward right. (So the ideal reaction condition is low temperature and high pressure?)
Enzyme nitrogenase can be used as alternative catalyst.
1. Active part is FeMo cofactor. (MoFe7S9?)
2. High amount of energy is required in form of high chemical potential of the electrons and hydrolysis of 16 molecules ATP per turn. (How to quantify this?)
3. Producing high chemical potential can be realized by provide H+ and e- instead of H2 directly. (Connect it to Ammonia Synthesis at Atmospheric Pressure, where H2 is dissociated into H+)
4. It is suggested that this can be accomplished by using proton conductor as electrolyte. But it is unknown whether enzyme has a structure that facilitates the proton transfer very well.

Ruthenium catalysts for ammonia synthesis at high pressures: Preparation, characterization, and power-law kinetics

Alkali-promoted Ru-based catalyst operates at mild conditions:
1. 70-105 bar pressure.
2. Lower temperature. (How low?)
3. Chlorine is poisoning during Ru based NH3 synthesis. Several chlorine free Ru catalysts have been studied.
Catalyst is found be inhibited by H2.

Hydrogen Production - Electrolysis of water and thermalchemical method

Hydrogen generation from water electrolysis-possibilities of energy saving

Current electrolysis cost and efficiency.
1. In most industrial electrolysers, energy consumption is 4.5-5 kWh/Nm^3 (nm^3 stands for normal meter cube)
2. The overall efficiency of the electrolyser is below 40%.

Summary of Electrolytic Hydrogen Production

Manufacturer Model	Energy Required - System (kWh/Nm3)	Energy Required - System (kWh/kg)	Energy Required - Electrolyzer (kWh/Nm3)	Hydrogen Production (Nm3/hr)	System power requirement (kW)	Conversion efficiency (%)	System efficiency (%)	Production Pressure (psig)
Stuart: IMET	4.8	53.4	4.2	60	288	80	73	360
Teledyne: EC-750	5.6	62.3	-	42	235.2	80	63	60-115
Proton: HOGEN 380	6.3	70.1	-	10	63	95	56	200
Norsk Hydro: Atmospheric Type No.5040 (5150 Amp DC)	4.8	53.5	4.3	485	2330	80	73	435
Avalence Hydrofiller 175	5.4	60.5	-	4.6	25	89	64	up to 10,000

Over 18% solar energy conversion to generation of hydrogen fuel; theory and experiment for efficient solar water splitting

At 25C, the water electrolysis potential (Vh2o) is 1.229V.
Efficient solar-driven water splitting requires a critical balance of the energetic of solar conversion and solution-phase redox processes.
Sensitization is required due to UV and visible light can transmitted through H2O. (Does this mean panel should be placed under water?)
Efficiency is defined by (efficiency of solar energy conversion)*(efficiency of redox)
1. Dual layered cell is made to test. The process is given in detail. Two layers are AlGaAs/Si.
2. Potential of photo (Vp) is the sum of bandgap of each layers.
  1. It is constrained by wide bandgap (Egw)+ small bandgap (Egs).
  2. It mus be greater than Vh2o.
3. Result shows 1.57 V open circuit potential is generated.
Except for ideal energy for electrolysis of water, over potential loss due to redox should be considered.
1. It depends on choice of electrodes (Any other dependence?)
  1. Pt(black) is observed to have less potential drop as electrode while with low level of convection to improve mass transport and prevent gas buildup on electrode surface.
  2. RuO2 are better suit for O2 side electrode with optimization of electrodes, including annealing, varying thickness, can decrease over potential loss.
Efficiency of redox can be as high as 90%-95%, major limit for total electrolysis efficiency is still efficiency of solar conversion.

Efficient Solar Water Splitting, Exemplified by RuO2-Catalyzed AlGaAs/Si Photoelectrolysis

Panel
Multilayers are grown. Top down: AlGaAs, p-GaAs, p+nn+ Si.

Antireflection: MgF2/ZnS.

P contact:Au-Zn/Au, n contact: Au-Sb/Au.

RuO2 and Ti are used as electrodes

~~Circuit~~
1. Both H2 and O2 electrode are optimized, parameter are almost the same as ones described in Over 18% solar energy conversion to generation of hydrogen fuel; theory and experiment for efficient solar water splitting It's exactly the same paper as Over 18% solar energy conversion to generation of hydrogen fuel; theory and experiment for efficient solar water splitting.

Photo-electrochemical hydrogen generation from water using solar energy. Materials-related aspects

Performance photo electrochemical cells (PECs) is considered in terms of:
1. Excitation of electron-hole pairs in photo-electrodes.
2. Charge separation in photo-electrodes.
3. Charge transfer (transportation?) in photo-electrodes.
4. Generation of PEC voltage for water decomposition.
Hydrogen as fuel is introduced in first part.
Photo electrodes are considered to be the key of conversion efficiency of photo-electrolysis.
Except for absorption of as much as possible solar energy, materials of electrodes of PECs is also considered to perform as catalyst for water decompostion. (How electrodes affect the efficiency of absorption?)
1. Band gap (~~multiple bandgaps?~~ Bandgap of electrodes. The optimal bandgap is 2 eV, however this is hard to get, closet material such as Fe2O3 is not suitable for aqueous condition.)
  1. TiO2 is currently (year 2002) the most promising material for electrodes. It has a bandgap of 3.2 eV.
  2. Doping TiO2 with V4+/V5+ can lower its bandgap.
  3. Silicon based multilayer electrodes is suggested. (Refer to Over 18% solar energy conversion to generation of hydrogen fuel; theory and experiment for efficient solar water splitting, but it is not suggested in that paper whether that electrodes can be immersed into water.)
2. Flat band potential. (What's this?)
3. Schottky barrier
4. Electrical resistance. Major electrical resistance loss are due to: electrodes, electrolyte, electrical wires, electrical connections, measuring and control equipment.
  1. Electrodes: using thin Ti film could reduce this resistance, also, Ti has a strong reduction potential.
  2. Electrolyte: H+ and HO- has the best mobility, but both of them are chemical aggressive. Cl- and NO3- are better choices.
  3. Helmholtz potential barrier. This is a barrier between semiconductors and liquid. Further information is still needed to be studied.
5. Corrosion
6. Microstructure (~~In concern of what?~~ While using polycrystalline, the properties of grain boundaries.)
7. Interfaces have a substantial impact on functional properties. (What function?)
8. At least one of two electrodes immersed into water should be semiconductor and absorbs light. (Why should it be immersed into water instead of just use normal cells and use separate electrodes?)
Efficiency of photo-electrochemical cell
1. Need to compare to using methane to produce hydrogen, which has already been commercialized. Technology still needed for electrolysis of water to improve efficiency.
2. Major energy loss
  1. PV panel associated loss. (In process of photo energy to activate electron.)
  2. Electron to chemical energy efficiency is only 75%, 25% is lost.
  3. Recombination of e-h, ohmic loss, over-potential loss in electrode/electrolyte interfaces.
3. Each term of efficiency is defined mathematically in paper.
  1. Solar conversion efficiency (c)
  2. Chemical efficiency (ch)
  3. Quantum efficiency (QE)
Hydrogen impact on environment and economics are discussed at last, along with its history.

Solar hydrogen production via a two-step water-splitting thermochemical cycle based on Zn/ZnO redox reactions

Two steps process has reached energy conversion efficiency of 29%, based on 90MW solar plant.
1. Using solar power to heat ZnO 2300K (~~Can solar provide this much high temperature?~~ Instead of using PV, this uses concentrated solar irradiation to directly heat ZnO2.), then ZnO is dissociated into Zn and O.
2. znO is directly exposed to high-flux solar irradiation.
3. At 700K, Zn react with water to form H2 and ZnO.
Efficiency is reported to reach 29% at 5000 solar concentration ratio, and 36% at 10,000 solar concentration ratio (How to define solar concentration value?)
Under reported efficiency, H2 production efficiency is 241 kJ/mol
H2 production and cost table is given, by which H2 prodcution efficiency and and invest/production ratio can be estimated.

Solar thermochemical production of hydrogen––a review

Thermochemical method use concentrated solar radiation to directly heat
1. Quantized as mean flux concentration ratio, in unit of suns.
2. Typical systems are trough (100 suns), tower (1000 suns) and dish system (10,000 suns).
3. Can be augmented by non-image concentrators.
4. Not as mature as solar electrolysis method (In what aspects?)
Cavity-receiver type, opening allows concentrated solar radiance is called aperture.
1. Incoming energy often greatly exceeds absorbance, due to reflection.
2. The larger cavity dimension to aperture ratio, the closer to blackbody absorber.
3. Smaller aperture will intercept more solar power. (Why not use lens to focus all radiance to what ever size of aperture?)
Several efficiency coefficient is defined. The higher the efficiency, the smaller the area is required to produce certain amount of H2.
Solar thermolysis for H2 from H2O
1. Single-step thermal dissociation of water is called water thermolysis, it requires temperature as high as 2500K.
2. Effective technique for separating H2 and O2 is required to avoid explosive. (Won't H2 react with H2 immediately after dissociation at 2500K?)
3. Several methods for separation are tested, but not found reliable.
Solar thermalchemical cycles for H2 from H2O.
1. Usually more than two steps
2. Inefficient due to heat transfer.
3. Recently, thanks to achievement of high temperature by solar (2000k), two step method has been developed.
  1. Step 1, use solar to dissociate metal oxide into metal and oxygen.
  2. Step 2, use metal (At what temperature?) to react with H2O to produce H2 and metal oxide.
  3. ZnO is considered to be the best metal oxide for this two step method currently, with energy efficiency of 29%.
Decarbonization of fossil fuels is discussed. (Will this fundamentally not a good idea since the final products include carbon oxide, to reduce which clean energy is widely studied?)
Economical assessments suggested thermalchemical method to produce H2 from H2O can be competitive against solar water electrolysis.

Thermochemical hydrogen production from a two-step solar-driven water-splitting cycle based on cerium oxides

Two step refers to:
1. Metal Oxide dissociates into metal and oxygen, using concentrated solar radiance as heat source.
2. Metal react with H20 and produce hydrogen and metal oxide.
Using ZnO, first step need 2300K while second step needs 900k.
Using CeO2 in cycle
1. First step, it requires 2000C (Which is 2273K, similar to the required temperature while using ZnO) and turns into oxygen and Ce2O3 instead of Ce.
2. Second step Ce2O3 react with H20 and produce H2 and CeO2, at 400-600C

Two-step water splitting thermochemical cycle based on iron oxide redox pair for solar hydrogen production

Advantage of iron oxide-based cycle:
1. Reversibility, which means high cycle efficiency.
2. Non-corrosive materials, avoids recombination during quenching.
Theoretical energy require to produce 1 mol hydrogen: 446.5 kJ (iron heating from 600C(Why this start temperature?) to 2100C.) + 64.9 kJ (water heating from 25C to 600C)
Iron oxide reduction
1. Hematite (Fe2O3) reduced completely above 1500C
2. Magnetite (Fe3O4)to FeO is more complex. 0.35% of sample mass is lost during this process.

Nitrogen Preparation

Since nitrogen generators has already been maturely developed, this part will be focused on study some devices in the market to decide which of them are better suited for this project. It is not known how nitrogen purity affect ammonia synthesis, but it is not that essential as hydrogen. Thus, although pressure swing absorption nitrogen generators usually provide more pure nitrogen, it will not be considered here, mainly because their high energy consumption and large scale. In the other hand, nitrogen membrane generators can provide nitrogen with acceptable purity at low energy consumption and flexible scales. These system will be considered to be reviewed here. All product must have output nitrogen purity greater than 99%.

IGS Skidded Nitrogen Generator

Product	Purity (%)	Input flow rate under 100 psig (ACFM)	Output flow rate under 100 psig (ACFM)
IGS Skidded Nitrogen Generators 7000 Series	99.9	129	60.2
Atlas Copco NGM 4	99.5	128.6	44.6

Industrial Grade Air Compressors

Compressors will be used in both inlets of nitrogen generator and ammonia convertor. However, the requirement for each inlet has huge difference. For nitrogen membrane system, the inlet air usually has pressure ranging from 100 - 500 psig, while the inlet syngas of ammonia syngas requires pressure as high as from 2030 psig to 3045 psig. Compressors usually measure power in horse power, 1 horsepower(HP) = 745.7 watts There are two categories of compressor will be examined:

For nitrogen membrane generator. Since membrane system generally can give a output of 250 Nm3/h at 100 psig, while the total N2 necessary for each acre of corn is no more than 114.32 Nm3 each year. So for this category, a compressor with pressure output of 100 psig, flow rate of 200 Nm3/h (126.8 ACFM) to 300 Nm3/h (190.2 ACFM)is desired.
For syngas of ammonia converter, the inlet gas usually has a pressure requirement from 2000 psig to 3000 psig. Similar like nitrogen compressor, since each acre of corn only requires no more than 457 Nm3/hr (290 ACFM) syngas, this is far less than the capacity of commercial compressor, so while consider this category of compressor, it won't be a critical parameter.

Compressor for nitrogen membrane inlet gas

Ring Power SULLAIR 3000V
Ingersoll Rand IRN37K-OF
FS-Circuit SE30
Quincy QGS 40

Product	Pressure (psig)	Flow rate (acfm)	Power (HP/kW)
Ring Power SULLAIR 3000V	100-175	176-132	40/30
Ingersoll Rand IRN50H-OF	100-150	200-159	>37
FS-Circuit SE30	100-175	129-94	30/22.37
Quincy QGS 40 [1]	100-125	189-177	40/30

[1] Quincy QGS 40 brochure does not explain the condition of its flow rate unit, simply give CFM, and here it is considered as CFM of FAD.

Compressor for ammonia converter syngas

Atlas Copco HX/HN

Product	Pressure (psig)	Flow rate (ACFM)	Power (HP/kW)
Atlas Copcp HX/HN	<2175 PSIG	76.5-3240	40/30-750/560

@@ Line 1: / Line 1: @@
- {{MY5490}}{{Lit}}
+{{MOST}}
+{{Lit}}
 This literature review supported the following publication:
 * Z. Du, D. Denkenberger, J.M. Pearce, Solar photovoltaic powered on-site ammonia production for nitrogen fertilization, ''Solar Energy'', 122, 562-568 (2015). http://dx.doi.org/10.1016/j.solener.2015.09.035 [https://www.academia.edu/18120043/Solar_photovoltaic_powered_on-site_ammonia_production_for_nitrogen_fertilization open access]
+ {{MY5490}}
 Ammonia synthesis is the most important step for nitrogen-fertilizer production and consumes approximately 1% of the world’s energy production and energy-related greenhouse gas emissions. In addition to the concomitant emissions caused by ammonia and nitrogen fertilizer synthesis, centrally produced fertilizer that must be distributed to farms also harms the environment because of the embodied energy of transportation. An environmentally-optimal nitrogen fertilizer system would be distributed on farms themselves using only renewable inputs. Recent developments in solar [[photovoltaic]] technology and subsystems for ammonia production have made non-organic on-site ammonia production physically possible. This study provides a technical evaluation of the process for on-site nitrogen-fertilization of corn using solar photovoltaic electricity as the energy input. The system consists of a water electrolysis system to generate hydrogen and a membrane system to generate nitrogen needed as material inputs. Total power consumption for syngas preparation to generate a unit of ammonia is calculated. System total energy consumption is calculated while compensating syngas preparation with heat recovery. Five case-study locations are evaluated to determine their suggested nitrogen fertilizer addition (N-rate) for corn growth and the energy consumption for suggested N-rate is calculated. The [[System Advisor Model]] (SAM) is then used to simulate the PV system output for those five locations. Finally, the PV land use required as a fraction of the corn field area is determined. The results indicate that because PV is so much more efficient at solar energy conversion than organic methods, even the worst case evaluated in Indiana requires less than 1% of the corn field converted to a PV system to provide enough energy to generate sufficient amounts of ammonia for fertilizer for the remaining corn. The system was modeled to provide ammonia to fertilize for corn fields larger than 1079 acres with the worst soil conditions, the area of which applies to more than half of cropland in the U.S. in 2011. As the finiteness and emissions of fossil fuel production of nitrogen become more important, this renewable system should become economical and future investigations into its overall viability are warranted.