FINAL EXAM BIOMASS

What are the key processes involved in biomass pretreatment?

Hydrothermal carbonization, gasification, pyrolysis.

What happens during hydrothermal carbonization?

Dehydration, decarboxylation, and polymerization of biomass.

What are the three hydrothermal conversion processes?

Hydrothermal carbonization (HTC), hydrothermal liquefaction (HTL), supercritical water gasification (SWG).

What is the main product of hydrothermal liquefaction?

Bio-crude oil.

Why are porous carbon materials significant in various applications?

They serve as catalyst carriers and adsorbents for pollutants.

What is pyrolysis?

The thermal decomposition of materials at elevated temperatures in the absence of oxidants.

What is the effect of temperature on pyrolysis product yields?

Higher temperatures produce more synthesis gas, while lower temperatures favor solid biochar.

What are the three types of pyrolysis?

Fast pyrolysis, slow pyrolysis, and flash pyrolysis.

What type of products does fast pyrolysis primarily produce?

A higher yield of liquid products.

What are the benefits of using hydrochar in soil?

Increases carbon content and improves soil fertility.

What are common applications for hydrochar?

Soil amendment, adsorbent in environmental remediation, fuel source.

What is pyrolysis in thermochemical conversion?

A process of chemically decomposing organic materials at elevated temperatures in the absence of oxygen.

Name two types of bio-oil reactors.

Bubbling fluidized bed and Circulating fluidized bed/Transport reactor.

What is a characteristic of a Bubbling Fluidized Bed reactor?

It requires small sizes of biomass and has good heat and mass transfer.

How does a Circulating Fluidized Bed reactor function?

Hot sand is circulated between a combustor and pyrolyzer, with heat supplied from burning char.

What is a feature of the Rotating Cone Pyrolyzer?

It has a compact design and does not require a carrier gas.

What disadvantage does the Ablative Pyrolyzer have?

It is complex and does not scale well.

Why is Vacuum Pyrolysis advantageous?

It operates at lower temperatures, avoiding adverse chemical reactions.

What is a drawback of the Auger Reactor?

It requires a hot sand heating and circulating system and has high wear and tear.

What are Microwave Pyrolyzers known for?

They are rapid, efficient, controllable, and provide uniform heating at the molecular level.

Describe the structure of Entrained flow reactors (gasifiers).

They operate at high temperatures and pressures with powdered fuel entrained in the gasifying medium.

What principle does conduction heat transfer rely on?

Energy transfer from high-temperature regions to low-temperature regions within a body.

How does convection heat transfer differ from conduction?

Convection involves the movement of air or fluid that carries heat away, whereas conduction does not involve fluid motion.

What is the mechanism of radiation heat transfer?

Heat is transferred through regions where a perfect vacuum exists by electromagnetic radiation.

What are essential phase change processes in heat transfer?

Condensation and boiling phenomena.

What is the log mean temperature difference (LMTD)?

It is the suitable mean temperature difference across a heat exchanger used in heat transfer calculations.

What is pyrolysis?

Pyrolysis is the thermal decomposition of materials at elevated temperatures in the absence of an oxidizing agent.

What are the three types of biomass pyrolyzers based on their operation?

They can be classified as fast, moderate, and slow pyrolyzers.

What is the effect of temperature on product yields in pyrolysis?

Higher temperatures typically produce more synthesis gas, while lower temperatures favor solid biochar production.

What products are generated from pyrolysis?

Products include gases, liquids (bio-oil), and solids (biochar).

What distinguishes gasification from pyrolysis?

Gasification occurs in an oxygen-lean environment with gaseous products as the target, while pyrolysis occurs without an oxidizing agent.

What operational conditions can affect the composition of pyrolysis products?

Reaction temperature and exposure time to heat affect product composition and yield.

What types of reactors are used in bio-oil production through pyrolysis?

Reactor types include bubbling fluidized bed, rotating cone pyrolyzer, and ablative pyrolyzer among others.

What is gasification?

Gasification is a thermal biomass conversion process where a controlled amount of oxidant reacts with biomass at elevated temperatures to produce combustible synthesis gas.

What are the main components of producer gas (syngas)?

The main components of syngas include CO, H2, CO2, CH4, N2, and H2O.

What are some advantages of gasification?

Advantages include feedstock and product flexibility, environmental superiority through pollutant control, reduced water consumption, and high efficiency with low CO2 production.

What are the steps of the gasification process?

The steps include drying, pyrolysis (or devolatilization), combustion, and reduction.

What do the combustion reactions in gasification produce?

The combustion reactions produce CO2 and H2O from the oxidation of biomass.

What is the significance of the water-gas shift reaction?

The water-gas shift reaction converts CO and H2O to CO2 and H2, which is significant for adjusting syngas composition.

What is the role of the oxidant in gasification?

The oxidant (e.g., air, steam, oxygen) provides oxygen for partial oxidation of biomass, generating heat and producer gas.

Name a common type of gasifier.

A common type of gasifier is the fixed-bed gasifier, where biomass forms a static bed through which the oxidant flows.

What are some common applications of syngas?

Syngas can be used for heat and power generation, or as a chemical feedstock for producing fuels (e.g., methanol, hydrogen).

What happens during the pyrolysis (devolatilization) step in gasification?

During pyrolysis, biomass is heated in the absence of oxygen, leading to the thermal decomposition of organic matter into char, tar, and non-condensable gases.

What is the process that mimics the natural formation of petroleum and natural gas in a laboratory setting?

Hydrothermal liquefaction

What are the main sources of petroleum and natural gas?

Tiny marine plants and animals that died and were buried on the ocean floor.

What geological conditions are necessary for the formation of oil and natural gas over millions of years?

Enormous heat and pressure causing transformation of remains.

What types of products are derived from petroleum?

Electronics, candles, paint, toiletries, energy, clothing, and more.

What happens during the hydrothermal liquefaction (HTL) reaction?

Hydrolysis, dehydration, dehydrogenation, deoxygenation, decarboxylation, repolymerization.

What factors influence the yield of biocrude in hydrothermal liquefaction?

Temperature, residence time, catalyst type, and feedstock-to-solvent ratio.

What is the aim of co-liquefaction in biomass processing?

To increase biocrude yield and control its composition/properties.

What are some examples of co-liquefaction feedstock combinations?

Microalgae and swine manure, rice husk and microalgae, various combinations of biomass and waste.

What is pyrolysis?

A thermochemical conversion process that involves the decomposition of organic materials at elevated temperatures in the absence of oxygen.

What is LMTD in heat exchanger design?

Log Mean Temperature Difference, a suitable mean temperature difference across a heat exchanger.

What is the correction factor used for?

It adjusts the LMTD for heat exchangers that are not of the double-pipe type.

What is the Venturi effect?

A phenomenon where a fluid's velocity increases and pressure decreases as it passes through a constricted section of a pipe.

What are electrostatic precipitators (ESP) used for?

Primarily for air pollution control, they polarize organic compounds to remove them from the air.

How does a Venturi scrubber function?

It utilizes the Venturi effect to remove pollutants from gases by creating a flow that captures particles in a fluid.

What is the purpose of a coalescing filter?

To combine small droplets of liquid into larger ones so they can be removed more easily.

What are the main components of a fluidized-bed reactor?

Feed system, feeder, high-temperature filter, condensers, and flow control valves.

What is the primary output of biomass gasification?

Syngas, which consists primarily of CO and H2.

What type of gasifier has high thermal efficiency and tolerates high moisture content?

Updraft gasifier.

In an updraft gasifier, which zone experiences drying?

The drying zone is between 100-200°C.

What is a major disadvantage of an updraft gasifier?

It produces low-quality syngas with high tar content.

Which gasifier design minimizes tar cleanup by converting tarry products into gas?

Downdraft gasifier.

What are the benefits of using a bubbling fluidized bed gasifier?

High throughput, good mixing, and high carbon conversion rates.

What is a significant limitation of downdraft gasifiers?

They require the solid fuel to be pelletized or briquetted.

What is a key characteristic of crossdraft gasifiers?

They are ideal for charcoal but have poor syngas quality.

What is the composition of conditioned syngas produced in gasification?

Typically includes CO, CO2, CH4, H2, and N2 in varying percentages.

What is the primary chemical property of hydrogen?

It burns with oxygen to form water.

From which Greek words is the name 'hydrogen' derived?

It means 'maker of water'.

What is the dominant method of hydrogen production in the US?

Steam methane reforming (SMR).

What is the main use of hydrogen in the United States?

Petroleum refining.

What is 'green hydrogen'?

Hydrogen produced through electrolysis using renewable energy sources.

What does the 'hydrogen economy' envision?

A future economic system where hydrogen is a central energy carrier, replacing or reducing reliance on fossil fuels.

What is the role of the water-gas shift reaction in hydrogen production?

It removes carbon monoxide and carbon dioxide during hydrogen production.

What is one key biological method for hydrogen production?

Bio-photolysis, where microorganisms use sunlight to split water.

Which technology combines steam reforming and partial oxidation?

Autothermal reforming (ATR).

What are the two methods for hydrogen production from biomass mentioned?

Thermochemical methods (gasification, pyrolysis) and biological methods.

What is biochar?

A carbon-rich product obtained from the thermal decomposition of biomass under limited oxygen.

Why is biochar modification vital?

It is essential for advanced applications and improving biochar properties.

What factors affect biochar properties?

Feedstock type and composition, pyrolysis conditions, post/pre-treatments.

What is a pre-modification approach?

Treating the feedstock or biomass with a modifying agent before the pyrolysis process.

What are the three types of biochar modification methods?

Physical activation, chemical activation, and biological activation.

How does physical activation modify biochar?

It modifies physical properties like size and porosity by methods such as ball milling or thermal treatment.

What are examples of chemical agents used in chemical activation?

Oxidizing agents, metal salts, acids, or alkalis.

What is the predominant process that occurs on the biochar surface?

Adsorption.

What are some applications of biochar?

Improves soil structure, nutrient retention, supports microbial activity, functionalized for adsorption, fuel briquettes, catalyst support, and additives in materials.