BIOCHAR PRIMER

DAVID CLAYBY A NON EXPERT

Ethanol vs Biochar

• Biochar vs ethanol

• Biochar produces a variety of products – Oil, gas, tar, heat, CO2– Stable carbon

• Ethanol– CO2, high quality feed, ethanol

Biochar• There may be a place for biochar

• Switching from slash and burn to slash and char techniques in Brazil can decrease both deforestation of the Amazon and carbon dioxide emission, as well as increase the crop yield.

• Under the current method of slash and burn, only 3% of the carbon from the organic material is left in the soil.

• With biochar we may increase this to 20 to 50%.

Biochar

• If the products we need are not high quality feed and ethanol

• This technology can be very low tech.

Biochar

• The lower the temperature, the more char is created per unit biomass.[60] High temperature pyrolysis is also known as gasification, and produces primarily syngas from the biomass.[61]

• The two main methods of pyrolysis are – “fast” pyrolysis , which yields 60% bio-oil, 20% biochar,

and 20% syngas, and can be done in seconds– “slow” pyrolysis can be optimized to produce

substantially more char (~50%), but takes on the order of hours to complete

Precision farming

• Biochar is relatively stable that can be used to increase the soil organic contents of eroded areas.

• The half live of biochar ranges fro 100 to 200 years, while the half life of fresh organic plant material.

• Adding these materials may make a longer term impact on the soil productivity.

Outline• What is Biochar?• How is it Made?

– Pyrolysis and Hydrothermal Carbonization Processes– Feedstocks– Yields

• What are its Properties?– Physical– Chemical

• How can it be Used?– Energy– Soil Fertility– Carbon Sequestration

• Where does it fit in the Environmental Technology Landscape?• Summary

What is Biochar?

• “Biochar is a fine-grained charcoal high in organic carbon and largely resistant to decomposition. It is produced from pyrolysis of plant and waste feedstocks. As a soil amendment, biochar creates a recalcitrant soil carbon pool that is carbon-negative, serving as a net withdrawal of atmospheric carbon dioxide stored in highly recalcitrant soil carbon stocks. The enhanced nutrient retention capacity of biochar-amended soil not only reduces the total fertilizer requirements, but also the climate and environmental impact of croplands.”

(International Biochar Initiative Scientific Advisory Committee)

What is Biochar?

• Product– Solid product resulting from advanced thermal

degradation of biomass• Technology– Biofuel—process heat, bio-oil, and gases (steam, volatile

HCs)– Soil Amendment—sorbent for cations and organics,

liming agent, inoculation carrier– Climate Change Mitigation—highly recalcitrant pool for

C, avoidance of N2O and CH4 emissions, carbon negative energy, increased net primary productivity (NPP)

How is Biochar Made?

• Major Techniques:– Slow Pyrolysis

• traditional (dirty, low char yields) and modern (clean, high char yields)

– Flash Pyrolysis• modern, high pressure, higher char yields

– Fast Pyrolysis• modern, maximizes bio-oil production, low char yields

– Hydrothermal Carbonization• under development, wet feedstock, high pressure, highest

“char” yield but quite different

Fast Pyrolysis Fluidized Bed Reactor

Pacific Pyrolysis Slow Pyrolysis SimplifiedProcess Flow Diagram

Pyrolysis

• Competition between three processes as biomass is heated:– Biochar and gas formation– Liquid and tar formation– Gasification and carbonization

• Relative rates for these processes depend on:– Highest treatment temperature (HTT)– Heating rate– Volatile removal rate– Feedstock residence time

Competition Among Pyrolysis Processes

• Factors favoring biochar formation:– Lower temperature– Slower heating rates– Slower volatilization

rates– Longer feedstock

residence times• In general, process is

more important than feedstock in determining products of pyrolysis

Feedstocks• Essentially all forms of biomass can be converted to biochar• Preferable forms include: forest thinnings, crop residues (e.g., corn• stover, alfalfa stems, grain husks), yard waste, paper sludge,• manures, bone meal• Trace element (Si, K, Ca, P) and lignin contents vary• Lignin content can affect char yields

What are the Properties of Biochar?Pine Wood Char

Corn Stover Char

Corn Cob Char

Physical Properties Change with HTT

Physical Structure andChemical Properties Dependon Carbon Bonding Network

13C CP-MAS NMRAmonette et al., 2008

Chemical Properties

• Slow Pyrolysis chars produced in presence of steam tend to be acidic (carboxylic acid groups activated)

• Fast Pyrolysis chars produced in absence of steam tend to be very basic and make good liming agents

How can Biochar Technology be Used?

• Generate Carbon-Negative Energy• Soil Amendment• Carbon Sequestration

Comparison of Biochar Production Methods

The Biofuel N2O Problem

• Recent work (Crutzen et al., 2007, Atmos.Chem. Phys. Disc. 7:11191; Del Grosso, 2008, Eos 89:529) suggests that globally, N2O production averages at 4% (+/- 1%) of N that is fixed

• IPCC reports have accounted only for field measurements of N2O emitted, which show values close to 1%, but ignore other indicators discussed by Crutzen et al.

• If 4% is correct, then combustion of biofuels except for high cellulose (low-N) fuels will actually increase global warming relative to petroleum due to large global warming potential of N2O

• Biochar avoids this issue– Ties up reactive N in a stable pool– Eliminates potential N2O emissions from manures and other biomass sources

converted to biochar– Decreases N2O emissions in field by improving N-fertilizer use efficiency and

increasing air-filled porosity

Carbon Sequestration• Why?

– Decrease atmospheric GHG levels

– Stop acidification of oceans by CO2 absorption

– We only have one Earth• How?

– Create stable C pool using biochar

– Use energy to offset fossil-C emissions

– Avoid emissions of N2O and CH4

– Increase net primary productivity (NPP)

Creating a Stable Carbon Pool with Biochar

Carbon Sequestration using Biochar

• Slow pyrolysis biochars are highly recalcitrant in soils with half-lives of 100-900 years

• Sensitivity analysis suggests that half lives of 80 years or more are sufficient to provide a credible C sink

• Recent evidence using 14C-labeled biochar shows no evidence for enhanced rates of soil humic carbon degradation in agricultural soils (Kuzyakov et al., 2009)

• No evidence for polyaromatic hydrocarbon (PAH) contamination has been seen

• Down-side risks seem very small

Soil Amendment• Biochar typically increases cation exchange capacity, and hence

retention of NH4+, K+, Ca2+, Mg2+• N from original biomass, however, may not be readily available• P, on the other hand, is generally retained and available• Liming agent• Enhanced sorption of organics (herbicides, pesticides, enzymes)

– (Good? Bad?)• Some evidence for increased mycorrhizal populations, rhizobial

infection rates• Used as carrier for microbially-based environmental remediation• Lowers bulk density

Low temperature (550 C)

High temperature

(650 C)

Increasing time

Low temperature (550 C)

High temperature

(650 C)

Increasing time

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10% soil

Switchgrass biochar pH

Processing temperature

pH

* 671 C

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Temperature

Atrazine sorption by switchgrass biochar

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Atrazine sorption by soil

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Atrazine sorption by corn stover biochar

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Atrazine

• Atrazine sorption is known to increase at when soil pH is either low (<5) or high (>8)

• The increased sorption (Kd) when biochar is present implies – Increased herbicide rates to get consistent weed control– Longer residence time at high pH (due to unavailability to soil

microbes)– Shorter residence time at low pH (due to chemical

hydroxylation)– Changed leaching potential

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2,4-D sorption by switchgrass biochar

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2,4-D

• 2,4-D is not a soil applied herbicide, however, small sorption coefficients to soil due to it’s negative charge give a model compound as comparison

• 2,4-D sorption also increased when specific biochar types were added– Less leaching by the negative compounds– Longer residence time

Where does Biochar Fit?• Offers a flexible blend of biofuel energy, soil fertility enhancement, and

climate change mitigation• Limited by biomass availability and, eventually, land disposal area• How much biomass can be made available for biochar production vs.• other uses?• Crop-derived biofuels cannot supply all the world’s energy needs

– Maximum estimates suggest 50% of current, 33% of future– Biodiversity (HANPP)?– N2O?

• Perhaps best use of harvested biomass is to make biochar to draw down atmospheric C levels and enhance soil productivity, with energy production as a bonus (but not the driving force).

• This will require government incentives (C credits?) and a change in the way we value cropped biofuels