Combustion Reactions and Fuel Characteristics

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Questions and Answers

What is the primary reason for feeding an excess of the less expensive reactant in a combustion reaction?

To ensure complete conversion of the valuable reactant (correct)

To reduce the pumping costs of the more expensive reactant

To increase the energy output of the reaction

To minimize waste products during combustion

What is the definition of theoretical air in the context of combustion?

The quantity of air required to contain enough oxygen for complete combustion (correct)

The total amount of air that includes excess air and the theoretical oxygen

The amount of air provided during actual combustion processes

The minimum moles of air required to sustain any combustion reaction

How can excess air be calculated if the actual feed rate of air is known?

By using the combustion ratio of the reactants

By multiplying the actual air feed rate by the conversion efficiency

By subtracting the theoretical air from the actual air feed rate (correct)

By dividing the actual air feed rate by the theoretical air feed rate

What happens during a combustion reaction if too much air is supplied?

Excess nitrogen in the air can lead to NOx formation Signup and view all the answers

What is true about the conversion of gas compositions from dry to wet basis?

It involves a procedure similar to converting mass fractions to mole fractions Signup and view all the answers

If 100 mol/h of butane (C4H10) is fed into a combustion reactor, what is required to calculate the theoretical O2 needed for complete combustion?

The stoichiometric equation for butane combustion Signup and view all the answers

In a combustion reactor, what does the phrase 'percent excess air' refer to?

The extra amount of air fed beyond the theoretical air required Signup and view all the answers

What is the main characteristic of charcoal?

Burns rapidly and produces no smoke Signup and view all the answers

What temperature range is soft coke produced in?

600-650⁰C Signup and view all the answers

What is a key characteristic of hard coke?

Produces significant smoke when burned Signup and view all the answers

What material are briquettes primarily made from?

Dust, culm, slack, and other waste remains Signup and view all the answers

What percentage of weight does bagasse constitute from virgin sugarcane?

20% Signup and view all the answers

Which of the following best describes briquettes?

Heat-resistant and hard Signup and view all the answers

Which characteristic is NOT associated with soft coke?

Contains a high percentage of volatile matter Signup and view all the answers

Why is charcoal widely used in countries like India?

It is effective for cooking purposes. Signup and view all the answers

What is a common use of hard coke?

Metallurgical processes Signup and view all the answers

What is a characteristic of metal hydrides regarding hydrogen storage?

They can absorb hydrogen gas up to 900 times their own volume. Signup and view all the answers

Which of the following is NOT classified as a liquid organic hydrogen carrier?

Water Signup and view all the answers

What type of materials can be used as sorbents for hydrogen storage?

Microporous organometallic frameworks Signup and view all the answers

Which statement about biomass is accurate?

It is a renewable energy source if used sustainably. Signup and view all the answers

What is the primary fuel source for sugar industries as mentioned?

Bagasse Signup and view all the answers

Why is biomass considered a sophisticated storage of solar energy?

It converts radiant energy into chemical energy through photosynthesis. Signup and view all the answers

What percentage of moisture is typically found in bagasse?

45-55% Signup and view all the answers

Which hydrogen production method accounts for the highest percentage of global hydrogen production?

Natural gas Signup and view all the answers

What is the calorific value of bagasse per kilogram?

2200 cal/kg Signup and view all the answers

What does the steam reforming process primarily produce?

Hydrogen Signup and view all the answers

Which of the following accurately describes the composition of bagasse referenced in the content?

45% C, 6% H2, 46% O2, 3% Ash Signup and view all the answers

What is the efficiency rate for separating carbon dioxide from natural gas for hydrogen production?

70-85% Signup and view all the answers

What are the two main factors driving the shift towards hydrogen energy?

Energy efficiency and sustainability Signup and view all the answers

What share of hydrogen production comes from electrolysis?

4% Signup and view all the answers

Which of the following sectors is NOT mentioned as involved in hydrogen energy utilization?

Agriculture Signup and view all the answers

What is the boiling point of hydrogen at one atmosphere pressure?

−252.8°C Signup and view all the answers

What is the main disadvantage of using liquefaction for hydrogen storage?

It has a low efficiency in energy input. Signup and view all the answers

Which hydrogen storage method utilizes adsorption principles?

Surface storage systems Signup and view all the answers

What is the energy input required to compress hydrogen from 1 to 350 or 700 bar?

9 to 12% Signup and view all the answers

Which of the following is NOT a category of materials-based hydrogen storage media?

Chemical storage systems Signup and view all the answers

What happens to molecular hydrogen in metal hydride storage systems?

It is absorbed into the metallic lattice. Signup and view all the answers

What is one of the challenges facing materials-based hydrogen storage systems?

Inadequate storage densities Signup and view all the answers

Which energy input ratio is typically higher for liquefaction compared to compression?

30% Signup and view all the answers

What is the role of heat in metal hydride storage systems?

Facilitates the charge and discharge of hydrogen. Signup and view all the answers

Which of the following statements about combined storage methods is true?

They can leverage both cooling and compression. Signup and view all the answers

Study Notes

Energy Sources

Air Required for Combustion: The net volume of air required for various constituents (CO, CH4, C2H4, C2H6, H) is calculated based on the stoichiometric ratio. The net air per cubic foot is 8.13.
Stoichiometric Combustion: This is the theoretical combustion of fuel with the exact amount of oxygen to produce only CO2 and H2O as exhaust products.
Air Composition: Air is primarily composed of oxygen (20.9%) and nitrogen (79.1%). Other trace gases are also present.
Hydrocarbon Fuel Combustion: Complete combustion of a hydrocarbon (CnHm) produces n moles of CO2 and (m/2) moles of H2O. This reaction is critical for combustion calculations.
Excess Air: Air is often supplied in excess of the theoretical amount needed for complete combustion.
Combustion Reactions: Combustion is the rapid reaction of a fuel with oxygen. Significant energy is released when common fuels such as hydrocarbons or carbon react with oxygen to form carbon dioxide and water. Partial combustion occurs when CO is formed from a hydrocarbon.
Types of Fuels: Common fuels used in combustion furnaces include coal, fuel oil, gaseous fuels (such as natural gas, methane), or liquefied petroleum gas (propane and butane).
Combustion Products: Combustion reactions will produce CO2, H2O, and potential CO and SO2.
Combustion in Reactors: Chemical engineers are frequently involved in the analysis of combustion reactors and their by-products, in addition to the production of heat management and control systems.
Examples of Combustion Reactions: The document provides examples of the complete combustion of carbon, propane, and carbon disulfide, noting that partial combustion of propane results in the formation of carbon monoxide rather than carbon dioxide.

Manufactured Solid Fuels

Charcoal: Derived from destructive distillation of wood, it burns rapidly with a clear flame and produces little to no smoke. It's used for cooking.
Coke: A solid residue from destructive distillation of coal. Two types, soft and hard coke, differ in temperature ranges during their production. Soft coke is used as domestic fuel and burns cleanly, whereas hard coke, produced at higher temperatures, gives off smoke and is used for metallurgical processes.
Briquettes: Made from waste material such as lignite, peat, coal, or coke dust. Good briquettes are solid, resistant to crumbling, and weather proof for storage and use.
Bagasse: Sugarcane residue from sugar processing, serving as a quick-burning fuel. It consists of fiber, sucrose, and water, with a significant amount of moisture. Improvements are being made to reduce the percent moisture content for increased efficiency.

Hydrogen Energy

Hydrogen Energy Generation: Major methods for producing hydrogen include use of natural gas, oil and coal, and electrolysis, with natural gas being the primary commercial method.
Steam Reforming: Steam Reforming is a method of producing hydrogen from natural gas using steam and a Nickel catalyst at temperatures between 700-1100°C.
Plasma Reforming: A hydrogen production method using a plasma arc to produce hydrogen from various fuel sources, including natural gas or liquified hydrocarbons. This method is designed to produce hydrogen and carbon black from fossil fuels. CO2 is not a byproduct.
Coal Gasification: Coal gasification involves a chemical reaction of coal with oxygen and steam to produce synthesis gas, a mixture rich in carbon monoxide and hydrogen.
Hydrogen Production from Water: Electrolysis uses an electrical current to split water into its components, hydrogen and oxygen, often using renewable energy.

Hydrogen Storage

Physical Storage: Hydrogen can be stored as a gas under high pressure or as a liquid at cryogenic temperatures.
Chemical Storage: Hydrogen can be chemically bonded to materials like metals (hydride storage) or stored in liquid organic carriers.
Surface Storage: Storage of hydrogen using materials with large surface areas, including MOFs, zeolites, and carbon nanotubes, where hydrogen adsorbs onto the surface.

Biomass Energy

Biomass: Organic materials from living organisms, including plants, animal waste, and agricultural residues (e.g., crop residues).
Biogas Production: A renewable energy source created through the anaerobic digestion of organic matter, producing primarily methane and carbon dioxide. Plant and animal waste are typically used as feedstock.
Biogas Uses: used for cooking fuel, electricity generation, and other purposes

Biodiesel

Biodiesel Production: Biodiesel is made biochemically from vegetable oil or animal fat via a transesterification process, leaving glycerin as a byproduct. The methyl esters, the biodiesel product, are used in diesel engines.
Biodiesel Sources: Various biological sources including recycled cooking oil, soybean oil, and animal fats are used to create biodiesel.
Biodiesel Applications: Biodiesel is compatible with existing diesel engines and is considered a renewable and environmentally friendly alternative to traditional diesel fuels.

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Description

This quiz covers various aspects of combustion reactions, including the role of excess reactants, theoretical air, and the conversion of gas compositions. Additionally, it explores the properties and production of different fuel types such as charcoal and coke. Mastering these concepts is crucial for understanding combustion processes in chemical engineering.