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Our waste-to-energy experts, pyrolysis experts, gasification experts, biochar experts, and torrefaction experts, are a world class group as these areas are vital parts of our business,  The Emerging Technology Division of Lee Enterprises consists of leading business, science, and technology experts in the conversion of biomass (and related materials, such as Municipal Solid Waste) into bioenergy, bioproducts and biofuels using the latest developing and emerging technologies.  Services include all aspects of commercializing innovation including strategic, operational, business development, and administration leadership, business and financial planning and analysis, financing strategies, techno-commercial evaluations, feasibility studies, evaluating the business preparedness and commercial potential of technology developers and their projects.  Such services are beneficial for inventors, entrepreneurs, investors, project developers, and public sector agencies involved in new technology, start-ups and early-stage ventures.  Our Waste-to-energy (WTE) consulting, pyrolysis consulting, gasification consulting, biobutanol consulting, biochar consulting, carbonization consulting, torrefaction consulting and hydrothermal consulting  is done by the top experts in the world!

What is Waste-to-Energy?

Waste-to-Energy, encompasses a wide range of technologies and processes.  Examples of wastes used to produce energy include biomass, municipal solid waste (MSW), food wastes, tires, and chemical wastes.  Processes include waste segregation, anaerobic digestion, incineration, pyrolysis, and gasification.

Waste-to energy projects have two process goals – diverting waste from landfills and converting the waste into a profitable energy product (steam, gas or electric power).  The choice of technologies is waste type dependent and also depends on local factors such as landfill costs (tipping fee or avoided cost), product value, public acceptance and environmental permitting.

Incineration is the most widely used process.  Municipal waste is incinerated and the heat is captured in steam generators and used to power steam turbines to produce electricity.  It has been deployed around the world for many years.  However, early deployment was associated with “belching smokestacks.”  This image has caused widespread public opposition to incineration.    Technically, it is reliable and cost effective.  However, getting incinerators permitted is all but impossible in many areas.

During the last 10 to 15 years, efforts have been expended to find non-incineration methods for diverting waste from landfills and capturing value.  Waste segregation has developed for MSW.  It is used to capture a substantial portion of the waste for recycling – certain plastics, paper, cardboard, and metals.  However, the residuals are still sent to a landfill.  The economics are dependent on large scale operations and close proximity to recycling centers.  This technology is not suitable in many small to intermediate size communities as the transportation costs to recycling centers can exceed the value of the product.

Anaerobic digestion is limited to select feedstocks and has not been widely adopted. Pyrolysis and gasification have evolved to fill the need for more robust processes that can handle a wide variety of wastes. However, of note, these processes can work in concert with waste segregation and nearly eliminate the need for landfill capacity. The processes can also process a wide variety of wastes with little or no process modification required. They are versatile in that they can also produce a variety of products to meet local needs. Lastly, the developers claim they can address smaller markets with capacities of a few hundred tons per day. Public acceptance is mixed. While more favorable than for incineration, there is still concern over toxic emissions. In reality, a properly designed gasification system can produce very low emissions – especially when the syngas is used for chemical synthesis.

The biggest disadvantage for both pyrolysis and gasification is market maturity and cost effectiveness. The processes are well understood. However, long term, reliable, economic operation at large scale (200 tons/day and above) has not been widely demonstrated.

What is Pyrolysis?

Pyrolysis refers to the decomposition or transformation of a compound caused by heat. Pyrolysis and gasification are two related process, differing mostly by temperature and process reactants.  As discussed in other sections, low temperature pyrolysis can be used to produce various products including torrefied wood, biochar and biocarbon.

High temperature pyrolysis is used for converting biomass or waste materials, (e.g., municipal solid wastes, tires, plastics), into electrical energy or other products.  The process is performed in the complete absence of oxygen and generally performed in the 800°C range.  The process thermally decomposes the organic materials into carbon char, combustible gases (carbon monoxide and hydrogen), and tars.

The gases and tars are often burned in a subsequent step using air as the oxidizer to produce steam for operating a steam turbine powered electric generator.  Care must be taken in a pyrolysis system to keep all equipment at high enough temperatures so that the tars do not condense on equipment where they can become a significant maintenance challenge.  The carbon char produced is co-mingled with the ash that is dependent on the feedstock material being pyrolyzed.  For example, municipal solid waste ash contains an ash fraction in the range of 20% to 25%. This ash-carbon residual is generally disposed in landfills and can have small quantities of hazardous metal constituents.  The cost of disposal negatively affects the process economics and can vary widely in different regions.

Public acceptance is an issue in many locations as fear of emissions is perceived with any high temperature process.  However, gas cleaning equipment can be used to minimize emissions. Pyrolysis units are treated much like an incinerator for permitting purposes.

What is Gasification?

Gasification is a process that converts organic or fossil based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide.  Pyrolysis and gasification are related processes differing mostly in temperature and process reactants with gasification conducted at significantly higher temperatures than pyrolysis (1000°C to 1200°C and higher).  Gasification thermally decomposes the organic feedstock into the three principal streams.  Steam is added to the gasifier as a chemical reactant to convert the carbon into carbon monoxide and produce additional hydrogen.  When steam is added, the process is referred to as steam reforming gasification.   The reaction products, mostly CO and H2, are called synthesis gas or syngas.  Gasification of coal at very large scale (1000 t/d) has been used commercially for many years for production of syngas as a chemical feedstock.

In the last 15 to 20 years, many companies have been developing smaller gasification systems (200 to 300 tons/day) for processing other feedstocks such as biomass, municipal waste, medical wastes, tires and chemical residuals.  Syngas from waste materials can be used as a fuel directly in a boiler to produce steam, in an internal combustion engine to produce electricity or as a chemical feedstock.  Uses for the syngas are heavily dependent on local economic factors such as natural gas costs, electrical power costs, and the need for syngas to produce liquid fuels.

Depending on the waste feedstock, the syngas may have contaminants -halogens and sulfur compounds – which must be removed prior to use as a chemical feedstock involving catalysts.  Even when used as a fuel, the presence of contaminants may require special equipment to minimize atmospheric emissions and for the combustion process to be compliant with air pollution regulations.  The ash from gasifiers is often converted to a liquid slag at operating temperature and has potential for beneficial use.  Public acceptance and permitting can be challenging in some areas of the country as the high temperature is associated with incineration.  A properly designed system has very low emissions.

The energy for these gasifiers can come from partial oxidation of the syngas or from energy sources such as a plasma arc.  Using a plasma arc minimizes diluents (CO2 and N2) and keeps the syngas at higher purity at the expense of using electrical energy.  The choice is an economic factor in syngas end use.  Plasma energy sources can be created by plasma torches or by using graphite arc electrodes as used in the steel industry.

What is Biobutanol?

Butanol is a four carbon straight chain primary alcohol which has gained enormous attention as a potential gasoline substitute in recent years.  This is due to its high energy density, low vapor pressure, low heat of vaporization and high hydrophobicity.  These promising physical and chemical properties of butanol make it suitable for blending with or direct substitution of gasoline.  Biobutanol can be produced through a fermentation process, using Clostridium acetobutylicum, which naturally produces acetone, butanol and ethanol in a 3:6:1 ratio.  Historically, however, it was produced from starch and was outcompeted by petroleum-based butanol production.

Biobutanol can occupy a significant portion of the advanced biofuel markets in the future, if economics of the fermentation process improve.  As a fuel, butanol has describable characteristics not shared by ethanol or fatty acid methyl ester biodiesel.  Its low vapor pressure and hydrophobicity (which minimizes water retention) allows its use in established gasoline infrastructure. Also, compared to ethanol, it has 30% more energy, and is less flammable.  It can be used in unmodified internal combustion engines blended with gasoline at any concentration (as opposed to 10%-15% for ethanol).  Its low vapor pressure facilitates its application in existing gasoline supply channels, and it is less hydrophilic, less volatile, less hazardous to handle, and less flammable than ethanol.  The ability to convert both hexose and pentose sugars provides a significant advantage over ethanol-producing yeast which can only consume hexose sugar.  This allows the use of a much wider variety of feedstocks, including low cost waste materials.

Butanol’s toxicity, low yield, and high recovery costs are the main challenges of production by fermentation.   Thus, despite its superior fuel properties, biobutanol does not yet enjoy the economies of scale of corn starch-based bioethanol production as it continues to be developed in a cost-per-unit-of-energy-produced manner.

What is Biochar?

Biochar is a name for charcoal when it is used for particular purposes.  Like all charcoals, biochar is created by pyrolysis of biomass. Specifically, biochar is produced from wood, using a higher temperature pyrolysis process as compared to the temperatures used for torrefaction and biocarbon production – 400°C to 500°C.  Biochar is used in agricultural applications as a soil additive.  When applied to soil, biochar acts as an agricultural catalyst by promoting plant growth but is not consumed.  Since it is a catalyst, its benefits continue for generations without further addition.

Biochar holds nutrients and fertilizers longer in the soil and provides other benefits which encourage plant growth while simultaneously sequestering the carbon. In other words, the carbon of the original biomass has been fixed and will not naturally return its carbon into the atmosphere for very long periods of time.  Biochar is one of the most promising agricultural breakthroughs since the discovery of fertilizers.

What is Carbonization?

Carbonization refers to the conversion of an organic substance into either carbon or a carbon-containing residue through pyrolysis or distillation. Above 3000°C, carbonization of biomass commences and the thermochemical reactions become exothermic (i.e., heat generating) which drives the higher-temperature pyrolysis with no (or little) external energy being applied.

Biomass undergoes major chemical modifications at these higher temperatures.  Carbonization mimics coalification whereby nature converts plant matter into coal.  However, where coalification takes about 300 million years, carbonization converts plant matter into biocarbon (closely related products are charcoal and biochar) in 300 minutes or less. Biocarbon has an energy density similar to bituminous coal – about 13,000 Btu/lb.  Biocarbon has the highest energy density among solid biofuels, and its chemical characteristics are most like coal.

The above process for the formation of biocarbon is also known as “slow” pyrolysis.  There is a related reaction commonly called “fast” pyrolysis, where the temperatures of carbonization are used but the material is heated very quickly and then quenched.  This restricts the formation of biocarbon which is a by-product of the process and the product, bio-oil (also known as pyrolysis oil), can be used as a liquid biofuel.

What is Torrefaction?

Torrefaction of biomass is best described as a low temperature pyrolysis where the organic material, typically wood, is heated in the absence of oxygen, producing a dry product with no biological activity like rotting. Torrified biomass is combined with coal to reduce emissions and increase the renewable fuel fraction of the power generated.

During the process, the biomass properties are changed to obtain a much better fuel quality for combustion and gasification applications.  During this process, oxygen-rich compounds are volatilized from the biomass. Torrefied wood is mainly composed of cellulose and lignin.  The torrefaction reaction begins at 200°C, but the practical range is 250°C to 280°C.  Care must be taken not to go much higher in temperature as carbonization begins in the range of 280°C to 300°C.  The volatilized materials are combusted to provide the heat for the process.  An optimum control point is autothermal operations where the energy of the volatiles is enough to supply the energy for the process.

The advantages of torrefied biomass pellets are:

1. Product is water-resistant; can be stored outdoors on a coal pile; and generally does not reabsorb moisture after drying.

2. The fibrous nature is reduced and the grindability is improved.

3. Energy density is higher than a wood pellet, especially on a volume basis.

4. No binder is necessary to form the pellet.

5. Biological degradation is greatly reduced.

6. Various biomass feedstock can be utilized.

7. Uniform quality improves combustibility.

What is Hydrothermal Upgrading?

Water above 100 °C changes from a liquid phase to a gas phase. One can change the temperature boundary by changing the pressure – a low pressure lowers the boiling point, similarly increasing the pressure maintains a liquid phase at higher temperatures than the boiling point – precisely why pressure cookers work so efficiently and why there is no water left on Mars as it is boiled away in the atmosphere.

Water, among some other substances like CO2 can also exist as a supercritical fluid. For water this boundary is right around a temperature of 374 °C and a pressure of 218 atm. At this point the boundary between liquid and gaseous phase water disappears and we get what is known in the technical jargon as a supercritical fluid. Academicians and researchers across the globe have found a plethora of catalyst-like uses for supercritical fluids. In the biofuels context, supercritical water in combination with a chemical catalyst deconstructs the organic polymeric backbone of the biomass into very desirable energy products and produces clean oil that is entirely fungible with the petroleum counterparts.

The grand challenge in the biomass to liquids (BtL) technology is to remove water from the material. It is the > 50% water content or as some like to define “the inherent wetness” of biomass limits the energy density and thus the energy value of most biomass feed. Removing “oxygen” content from the highly functionalized biomass feed while maintaining or retaining maximum “carbon” is a major challenge in the field.

Using supercritical water to deconstruct biomass can be looked upon as a complementary technology towards the more traditional pyrolysis or gasification processes. While the impact of these processes are similar, one obtains a lot more oil as a product and there is usually no methane and no biochar, in addition one may use biomass straight from the fields circumventing the energy intensive pre-drying step. What makes this process different is that there are no polyaromatics, and the product can be processed in a conventional refinery. The resulting water stream generated from the HTU process would consist of valuable chemicals such as low-molecular weight aliphatics, lignin monomer molecules, oxidised lignin monomers, aromatic diacids, aromatic polyols, quinones, aromatics, O-heterocyclic compounds, and phenolics. A few of the commercially important aromatics can be seen in Table 1.

The HTU process offers a unique pathway to a product that can substitute a major portion of the products obtained from conventional crude oil spectrum. The process is well defined for forestry, agricultural waste, wood, paper/pulp waste, and algae and is competitive with $50 oil based on $100 per ton biomass – economically right in the sweet spot with enough margin to make the risk-return attractive. Figure showing HTU. With the highly experienced consultants at Lee Enterprises Consulting Inc., we are able to offer insight into this niche technology and further upgrading technologies for commercial partners.

Table 1. A few commercially relevant aromatic compoundsa

Compound Application
Benzoic acid Rubbers, preservatives, dyes
Catechol Printing, photochemicals, pharma, corrosion inhibitors
Benzaldehyde Fragrances
Vanillin Flavour, food
Hydroquinone Antiseptics, photography, inhibitors, skin bleaching agents
1,4-dimethoxybenzene Solvents, food, antioxidant
4,4’-biphenol Rubbers, plastics
1,2-dimethoxybenzene Synthetic precursor, food
2-methoxyphenol Synthetic precursor to eugenol, vanillin, food
p-cresol Synthetic precursor to antioxidants, solvents

aProduced at levels greater than 1,000 tonnes per annum and are priced greater than ≥1800 USD/t

HTU:

  • Feedstocks: forestry, agricultural waste, wood and paper/pulp waste, algae
  • Conditions: Temperature: 300 – 350 °C; Pressure: 120 – 180 bar, Time: 5 – 20 minutes, Solvent: liquid water present, Catalyst, Thermal Efficiency: 70-90%
  • Chemistry: Removing “Oxygen” from biomass as “Carbon-dioxide” and “Water”
  • Products:
    • 45% biocrude (%w on feedstock)
    • 25% gas (>90% CO2 remainder CO, lower alkanes e.g., methane, ethane etc.)
    • 20% H2O
    • 10% dissolved organics (e.g., acetic acid, ethanol, low-molecular weight aliphatics, oxidised monomers, aromatic diacids, aromatic polyols, quinones, aromatics, O-heterocyclic compounds, and phenolics)