Q2. What are the contributions mentioned in the paper "Valorisation of rice husks using a torbed® combustion process" ?
In this paper, the authors investigated the feasibility of using rice husk ash in a TORBED reactor across a wide temperature range.
Q3. What are the future works mentioned in the paper "Valorisation of rice husks using a torbed® combustion process" ?
It must be noted that even if these conditions could be met, it is possible that in the future, the proper costing or capture of environmental externalities would not allow projects such as these to proceed.
Q4. What is the way to increase the digestion rate of RH?
Further optimisation of the combustion process to generate higher surface area material might be necessary to increase the digestion rates further.
Q5. What is the effect of the ratio of Na2O/SiO2?
It is likely that, because the ratio of Na2O/SiO2 ratio increases at lower solids loadings, the OH ion concentration is not depleted as quickly, which enables faster reaction at longer reaction times.
Q6. How long did the economic evaluation of a hypothetical power plant take?
The economic evaluation of a hypothetical power plant fired by RH was carried out using a discounted cash flow method over a period of a 30 year project life span.
Q7. What is the potential of the RH produced in Thailand?
even for their more prosperous and energy hungry neighbour, Thailand, the RH generated each year has the potential to meet around 3% of the annual electricity demand.
Q8. What is the effect of surface reaction on silica?
Mgaidi [22] state that because the reaction between sodium hydroxide and silica is a surface reaction, only a small proportion of the solid is in contact with the liquid.
Q9. What is the typical process for making sodium silicate?
Traditionally sodium silicate is made by fusing silica sand and sodium carbonate together at 1400°C which is highly energy intensive.
Q10. What is the effect of surface area on the silica?
It is likely that the greater surface area of the samples produced at lower temperatures increases the silica exposure to the reacting sodium hydroxide.
Q11. Why is the RH gas velocities so high relative to a fluidised bed?
Because of the recirculating action of the EBR, the gas velocities that can be passed through are extremely high relative to a fluidised bed.
Q12. What is the effect of using 2M sodium hydroxide in the RHA?
To obtain total conversion of the silica in the RHA, it appears that using 2M sodium hydroxide is insufficient at the reaction conditions studied herein.
Q13. What is the main explanation for the reduction in surface area of the ash?
Three potential explanations for this behaviour can be postulated: (1) at higher temperatures, gasification reactions explode the internal structure of the RH leading to a decrease in pore volume [16]; (2) the adhesion of the silica particles to each other increases as the temperature increases; and (3) that the carbon content of the lower temperature ashes is providing most of the porosity.
Q14. How many temperatures can be used to combust a parboiled RH?
The current paper documents the use of a TORBED reactor to combust a parboiled RH from Arkansas, US at a series of six temperatures ranging from 700-950°C.
Q15. How long does it take to crystallise silica?
RHA silica can remain in amorphous form if temperature is < 900°C and residence time is < 1 hour or it crystallises if the temperature > 1000°C and residence time is > 5 min.
Q16. What is the main advantage of the RH combustion process?
This has several benefits but pertinent to RH combustion is the small load in the reactor, which enables a very fine temperature control.
Q17. What is the potential economic benefit of the ash?
This is of potential economic benefit in utilisation of the ash, as it minimises the grinding that might be required by a particular application.
Q18. What is the evidence of cristoballite in the XRD pattern?
Even when combusting at the highest temperature studied (950°C), there is evidence of only a small amount of cristoballite in the XRD pattern.
Q19. Why does the RH surface appear smooth and glassy?
The outer surface of these particles appears relatively smooth and glassy, whereas the particle interior retains much of the fibrous porosity of the parent RH.
Q20. What is the importance of the avoidance of the inhalation of RH?
The avoidance of the inhalation of this powder is a vital health and safety issue, not only to plant operators, but also to local inhabitants.
Q21. What are the temperatures for limiting the crystallisation of silica?
Reported optimal temperatures for limiting the crystallisation of silica within the literature vary widely: < 725°C [10]; limited crystallisation at 700°C [11]; and < 900°C [12].
Q22. What is the way to digest crystalline silica?
It is also much easier to digest in alkaline medium than crystalline silica and this potentially represents a gentler route for the production of sodium silicates and/or synthetic zeolites [5].
Q23. Why is the silica in the RH so large?
The images suggest two things: (1) the silica in the parent RH has not melted into a structure of sufficiently low viscosity to form spherical ash particles as often observed in fly ash originating from coal [14]; and (2) the silica has instead fused together in its original morphological form to provide the network of very large pores (1-10 µm) that are dominant.
Q24. How much does the rate of silica dissolution slow?
once the conversion of silica reaches 60%, the rate for all samples slows significantly, and there is little difference between them.