Tema 5 Pyrolisys

A biomass feedstock with a low H/C ratio is subjected to pyrolysis under externally supplied heat. Which statement best describes the combined effect on reaction thermodynamics and product distribution?. The process becomes exothermic due to increased carbon content, leading to higher hydrocarbon gas production. The process remains net endothermic, with increased char formation due to limited hydrogen for volatilization. The process becomes self-sustaining as unsaturated hydrocarbons release heat during formation. The process produces mainly saturated liquids due to enhanced hydrogen recombination.

Why can performing gasification after fast pyrolysis be advantageous in biomass upgrading processes, compared to directly using pyrolysis products?. It increases the stability and energy content of bio-oil without further processing. It enables the conversion of oxygen-rich and complex compounds into simpler and more versatile syngas components. It reduces the need for high temperatures in the overall process. It eliminates the formation of gaseous products.

Which of the following properties of bio-oil most limits its direct use as a substitute for conventional fossil fuels?. Low sulfur content. High oxygen content. High volatility. Low density.

An oil shale deposit is located at a depth inaccessible to surface or shallow mining, surrounded by a formation that has low permeability . The kerogen content is around 9%. Based on those characteristics, which of the following outcomes would most likely result from attempting ex situ retorting on this deposit ?. It would be the best approach as ex situ offers high recovery rates of organic matter regardless of the depth or the richness of the deposit. It would succeed moderately as ex situ has a relatively straightforward control of process operating variables that would compensate the low level of kerogen. It would be impractical as the insufficient permeability in the formation would cause poor subsurface combustion control. It would be unfeasible, as ex situ is limited to rich shales accessible to surface or shallow mining and requires high capital investment.

In pyrolysis processes, product distribution depends strongly on operating conditions. Which of the following process conditions favors the formation of char as the main product?. High heating rate, high temperature, and short residence time. Low heating rate, low temperature, and long residence time. High heating rate, intermediate temperature, and short residence time.

What mechanism is mainly responsible for the formation of gold hydrogen in the Earth’s crust?. The action of sunlight on water in the ground. The reaction between water and certain iron-rich rocks. The combustion of organic matter underground. Air pressure in underground cavities.

Pyrolysis is a thermochemical process that converts biomass into different types of fuels. Depending on the process conditions, which types of products are typically obtained from the pyrolysis of a solid fuel?. Only carbon dioxide (CO2) and water vapor (H2O),. Only ash and inorganic residues. Bio-char, bio-oil/tars, and a mixture of gases,. Liquid gasoline and pure oxygen (O2).

Which Pyrolysis process produces liquid as main product?. Slower heating rate, lower temperature, and longer residence time. Higher heating rate, higher temperature, shorter residence time. Higher heating rate, intermediate temperature, short residence time. Slower heating rate, intermediate temperature, and longer residence time.

Which of these is NOT one of the three main products of pyrolysis?. Syngas (gas). Lignin. Char (solid). Bio-oil (liquid).

What physical limitation can prevent a biomass particle from actually reaching the very high heating rates required for fast pyrolysis, even when the reactor supplies enough external heat?. The low thermal conductivity of biomass, which limits how quickly heat penetrates into the particle interior. The high chemical reactivity of biomass, which promotes self‑heating and accelerates the internal heating rate. The release of moisture at low temperatures, which generates internal steam and increases the heating rate. The fact that pyrolysis is generally autothermal, eliminating the need for efficient heat transfer.

When solid organic matter is heated in the absence of oxygen, the balance between char, liquid, and gas depends strongly on the severity of the thermal treatment. Which of the following statements correctly identifies how increasing temperature generally affects the product distribution in both biomass pyrolysis and kerogen cracking?. Higher temperatures tend to increase gas production at the expense of liquids and char. Higher temperatures always increase liquid yields because more material melts. Higher temperatures favour char formation because the solid becomes more stable. Temperature has no significant effect; only pressure determines the product distribution.

Biomass contains a significant amount of oxygen in its chemical structure. This oxygen strongly influences the type and quality of the products formed during pyrolysis. Which option describes better the impact of oxygen on pyrolysis products?. Most of the oxygen in biomass remains in the char, increasing its heating value. The oxygen in biomass is mainly transformed into light hydrocarbons, increasing gas yield and the energy content of the gaseous products. Part of the oxygen in biomass is converted into water, CO and CO₂ , decreasing the heating value and stability of the bio-oil. Oxygen is almost entirely removed during heating and therefore has no relevant impact on product distribution.