|The Virent 10kW APR/HICE demonstration system, in service with MG&E.|
In a demonstration of the capability of its Aqueous Phase Reforming (APR) process, Virent Energy Systems announced the successful startup of a 10kW power generation system that converts sugars and glycerin directly into hydrogen and natural gas as fuel for a Ford 1.6-liter, four-cylinder combustion engine genset.
This is the first production demonstration of a system of this type, and promises a more energy-efficient mechanism for the direct conversion of bio feedstocks into hydrogen and other fuel gases than current thermoconversion technologies.
The demonstration system, purchased by Madison (Wisconsin) Gas & Electric (MGE), is based on Virent’s patented Aqueous Phase Reforming (APR) process, a carbon-neutral, one-step method for on-demand production of hydrogen, natural gas and/or other fuel gases for distributed power systems from fuel stocks derived from widely available renewable biomass.
The level of excitement generated by this APR system start-up is very high because the system greatly exceeded all of our targets for power output and performance with an integrated ICE. It is very clear that the APR system represents a compelling option for cost effective, clean, distributed energy generation.
With the global availability of CO2 neutral feedstocks and the ability to fuel microturbines, fuel cells, and ICEs in an untethered fashion, the market opportunities are enormous.—Eric Apfelbach, CEO Virent
|The APR process. Click to enlarge.|
Aqueous Phase Reforming. Virent’s APR system offers a cost-effective method for low-temperature (180º–260º C) production of hydrogen and/or fuel gas from oxygenated compounds, such as ethylene glycol, biomass-derived glycerol, sugars and sugar-alcohols. The APR systems can be designed to deliver predominantly hydrogen or alkanes (natural gas, ethane, butane and propane), or a customized blend of these fuels (which Virent has tagged with the term “Supernatural Fuels”).
Modification of the catalyst and/or the temperature of the process modifies the composition of the resulting gas. For example, in earlier work Virent founders discovered that the aqueous-phase reforming of sorbitol, glycerol, and ethylene glycol solutions produced an effluent gas stream composed of 50-70 mol% H2, 30-40 mol% CO2, and 2–11 mol% alkanes (dry basis) at high conversion.
Addition of Sn (tin) to Ni (nickel) in the catalyst improved the selectivity for production of H2 by ethylene glycol reforming from 35% to 51% at a Ni:Sn ratio of 270:1, while the alkane selectivity was reduced from 44% to 33%. At a Ni:Sn ratio of 14:1, the hydrogen selectivity increased to 90%, while alkane production was nearly eliminated.
The efficiency of the reactor and the composition of the output also depends on the nature of the feedstock. Virent has found that while the selectivity for hydrogen production is insensitive to different concentrations of sugar-alcohols such as sorbitol, hydrogen selectivity from the reforming of glucose decreases as the liquid concentration increases from 1 to 10 wt% because of undesired hydrogen-consuming side reactions that occur in the liquid phase.
The addition of a Pressure Swing Adsorption (PSA) system or palladium membrane to the process could produce hydrogen pure enough for use in fuel cells. Such systems are easily integrated into the APR process, especially since the gas leaves the reactor at 400–500 psi.
The APR process offer a number of cost and efficiency benefits:
It generates hydrogen without the need to produce high-temperature steam, which represents a major energy saving over other multi-step processes for the generation of hydrogen from hydrocarbons;
It is efficient in its use of catalyst. APR processing of sorbitol at 215º C over a platinum-based catalyst will generate about 15 watts H2/gram of catalyst. A conventional high-temperature, multi-step process generates about 1 watt H2/gram of catalyst, according to Virent. Put another way, APR generates about 15 times more hydrogen per mass of catalyst than existing steam reforming process.
It occurs at temperatures and pressures where the water-gas shift reaction is favorable, making it possible to generate hydrogen with low amounts of CO (less than 100 ppm) in a single chemical reactor;
It occurs at pressures (typically 15 to 50 bar) where the hydrogen-rich effluent can be effectively purified, if desired, using either pressure swing adsorption or membrane technologies;
It takes place at low temperatures that minimize undesirable decomposition reactions typically encountered when carbohydrates are heated to elevated temperatures;
It uses widely available bio feedstocks or by products of other biofuel processing (i.e., the glycerin produced from the biodiesel production process.
The demonstration system. The MGE system integrates a Virent APR System with a hydrogen/natural gas fueled generator set provided by City Engines. (Earlier post.) The system has demonstrated the ability to deliver a minimum of 10kW of power to the MGE grid since its startup at the beginning of this year at Virent’s location in Madison, Wisconsin.
Virent customized the gas production from its APR system to deliver an effluent gas composed of approximately 30% hydrogen; 10% methane; 10% ethane; 10% propane; and 40% CO2. (The CO2 vents to the atmosphere, but as it is derived from biomass, is greenhouse neutral.) Gas flows into the engine at the rate of 90 liters/minute.
City Engines modified the 1.6-liter engine to run on a gaseous mixture of about this type. Although fine-tuning is still underway, the engine is performing well and has delivered efficiencies as high as 38% on the genset at 10 kW, according to Apfelbach. (Virent is claiming an overall 32% efficiency.) The engine has an electronic control feature so to allow for the easy tuning of the fuel/air ratio and timing.
Virent has not yet measured the emissions from the system, but expects them to be comparable or slightly lower than those from engines running hydrogen-CNG mixtures (HCNG).
The exhaust heat from the engine is recycled as process heat for the APR. The system may require the burning of about 10% of the gas stream to add more heat at lower power levels.
Currently the APR system is using a 50% concentration of gylcerol as the feedstock, consuming it at the rate of 2.2 gallons/hour. In the future, Virent will use a lower grade of glycerol that is generated as a byproduct of the biodiesel production process. Virent also intends to use sugar in the form of sorbitol and glucose as a feedstock for this initial unit. (Sorbitol or glucose will have slightly less net efficiency.)
We are proud to have played a role in the first ever demonstration of direct conversion of biomass derived liquids to fuels. This furthers our commitment to finding clean sources of fuel from renewable sources. We think the Virent process holds the potential for reshaping how people think about renewable energy.Gary Wolter, MGE Chairman, President and CEO
Futures. Virent is in the early stages of commercializing this work, and the demonstration (beta) unit will go through numerous refinements as the project team gathers data and tweaks the system.
However, the prospect of producing CO2-neutral hydrogen and fuel gas out of renewable feedstocks with greater efficiency is a compelling proposition with implications for many markets and uses.
As an example, one possible application Virent is exploring is the production of “green LPG” for vehicle fuels—the APR can process glucose (a six-carbon sugar) with fairly high selectivity to propane (3 carbon alkane) and butane.
|APR versus Reforming Ethanol|
|Corn to Ethanol||H2 from Ethanol||APR: Corn to H2|
|Gross Energy Produced (BTUs/bushel)||196,042||230,702||230,453|
|Process Energy consumed (BTUs/bushel)||134,625||232,646||80,659|
|Net Energy (BTUs/bushel)||61,417||-1,945||149,794|
|Production Output/Input Ratio||1.46||-0.04||2.86|
As another example, taking corn to hydrogen via the APR rather than processing corn to ethanol delivers more than 2.4 times the BTUs per bushel of crop, according to Virent’s calculations. That includes the wet mill processing of the corn to produce the input sugar solution for the APR.
The cost of the process will largely be driven by the cost of the sugar feedstock. One reason Virent is working with glycerol is the glut being put on the market by biodiesel manufacturing. For every 10 pounds of biodiesel produced (about 1.4 gallons), one pound of glycerol is produced. For every 10 lbs of glycerol, Virent can generate 1 lb of hydrogen or 3 lbs of alkane fuel gas.
Or, to put it in another context, 20 gallons of 70% liquid sugar could produce sufficient hydrogen to take a Honda FCX 350 miles, according to Apfelbach. The hydrogen, with today’s sugar prices, would cost less than $3/kg.
Virent technology presentation
“Production of Liquid Alkanes by Aqueous-Phase Processing of Biomass-Derived Carbohydrates”; George W. Huber, Juben N. Chheda, Christopher J. Barrett, James A. Dumesic; Science 3 June 2005: Vol. 308. no. 5727, pp. 1446 - 1450 DOI: 10.1126/science.1111166
“Raney Ni-Sn Catalyst for H2 Production from Biomass-Derived Hydrocarbons”; G. W. Huber, J. W. Shabaker, and J. A. Dumesic; Science 27 June 2003 300: 2075-2077 [DOI: 10.1126/science.1085597]