Municipal Solid Waste Cofiring in Coal Power Plants: Combustion Performance

The combustion of fuel derived from municipal solid waste is a promising cheap retrofitting technique for coal power plants, having the added benefit of reducing the volume of waste disposal in landfills. co-combustion of waste-derived fuel (WDF) and coal, rather than switching to WDF combustion alone in dedicated power plants, allows power plant operators to be flexible toward variations in the WDF supply. Substituting part of the coal feed by processed high calorific value waste could reduce the NOx, SO2, and CO2 emissions of coal power plants. However, the alkaline content of WDF and its potentially harmful interactions with the coal ash, as well as adverse effects from the presence of chlorine in the waste, are important drawbacks to waste-derived fuel use in large-scale power plants. This chapter reviews these points and gives a centralized review of co-combustion experiments reported in the literature. Finally, this chapter underlines the importance of lab-scale experiments previous to any large-scale application and introduces the idea of combining waste and additives dedicated to the capture of targeted pollutants

Induction heating fluidized bed reactor for coal-based cofiring tests

Cofiring of coal plus a sulphur free feedstock i.e. municipal waste in fluidized bed reactors has been an interesting pathway to reduce SOx emissions where, for example, economical alkali (Na or K) or earth alkali (Ca) bearing sorbents are added to the cofiring feedstock. However, a large array of cofiring feedstock and sorbent formulations are normally generated to find the optimum operating conditions in terms of maximum emissions reduction and prevention of defluidization state. The latter occurs due to either the inorganic content of the feedstock or the alkali components of the feedstock that combine with the bed material forming low temperature melting eutectics at the surface. Occurrence of the defluidization state in a large-scale fluidized bed reactor causes a lot of operation delays due to overhaul, reactor cleaning and bed material loading. Performing such high temperature screening tests, between 800 and 1200 °C, in the pilot reactors is very challenging, labour demanding and costly. On the other hand, the available micro reactors have limitations to mimic cofiring conditions in the large-scale reactors. The novel Induction Heating Fluidized Bed Reactor (IHFBR), 2.5 cm diameter and 7.5 cm height, provided a fast heating rate, quick and accurate solid feeding technique, durability at extremely high temperatures, and convenient operation making it ideal for a large set of coal-based cofiring screening tests. It was also discovered that the defluidization state could be easily predicted. Therefore, a considerable amount of time and cost, i.e. cost of material, operation and equipment was saved

Catalytic ash free coal gasification in a fluidized bed thermogravimetric analyzer

Catalytic ash free coal gasification was investigated in the newly developed fluidized bed thermogravimetric analyzer. The total yield obtained from the fluidized bed TGA showed good agreement with the total gas product. For char gasification, the values of activation energy and pre-exponential factor were similar to those obtained from coal gasification in our previous work. The activation energy for the CO shift reaction decreased by 56% and 37% from the value reported in our previous work for coal gasification and in literature for catalytic coal gasification respectively. For the methane reforming reaction, the value of the activation energy was reduced by 33% from the one observed previously in our work, in the absence of a catalyst and decreased by 42% from the one reported in literature for catalytic gasification. The carbon conversion for the catalytic ash free coal gasification was 69% higher than the value obtained from the coal gasification for the same experimental conditions. This value was found to be 44.5% for the ash free coal gasification. The heating value of the gas product by using the catalyst for temperatures below 520°C was also higher than without catalyst. However, at higher temperature, using the catalyst had no effect on the heating value of the gas product

Improving resource efficiency to address climate change by observing nature

This presentation will discuss the climate change challenge and how it needs to be addressed by closing the resource loop. More specifically, a parallel will be drawn between what we have done since the beginning of the industrial era and what nature can teach us on addressing waste recovery. We will see that nature, by design, reutilizes all the resources since the resources on the planet are finite: there is no incoming feed of new material from the Universe to replace what has been consumed. However, energy is abundant, free and available everywhere through solar radiation. This is why evolution was more favorable to systems that could work together at recycling all atoms, without primarily favoring the energy efficiency of those systems. This is in direct contrast to our industrialized world where energy has a cost, because it is resource–derived, which forces us to be primarily energy efficient. In most cases, recovering waste requires work to reorganize the matter and our focus on energy efficiency immediately discards any attempts or processes that would require energy to convert waste. Billions of years of evolution show that the best and yet most efficient system for closing the loop of carbon requires energy and is called photosynthesis. Perhaps this tells us that the “holy grail” technology everybody is looking for, which would use minimal energy to recycle material, might not be possible. Certainly, this should guide our approach towards recycling. Please click Additional Files below to see the full abstract

Similarities between gas-solid fluidization in the presence of interparticle forces at high temperature and induced by a polymer coating approach

The hydrodynamics of gas-solid fluidized beds at high temperature is a critical factor in their design and operation. Nevertheless, the present understanding is far from satisfactory due to the lack of insight about the relative importance of interparticle forces (IPFs) and hydrodynamic forces. Owing to the global trend of processing lower quality feedstock in high temperature gas-solid fluidized beds, which can result in the accumulation of low melting point eutectics in the bed, focusing on the evolution of IPFs at elevated temperatures is essential. The harsh experimental conditions at high temperature only allow for the application of a limited number of measurement techniques for the purpose of hydrodynamic study. A polymer coating approach (1), however, can be adopted to reproduce the conditions of a high temperature gas-solid fluidized bed at near-ambient conditions. This technique employs inert base particles coated with a polymer having a low glass transition temperature. With this method, varying degrees of IPFs can be deliberately and accurately adjusted in the bed through controlling the inlet air temperature. This study aimed to explore the capability of the polymer coating approach in highlighting the influence of IPFs on the bed behavior in a much friendlier environment compared to a high temperature fluidized bed. The polymer coating approach was employed in the first experimental step to attain fluidized beds with different levels of IPFs at near-ambient conditions. The second experimental step focused on the hydrodynamics of gas-solid fluidized beds at elevated temperatures in the presence of IPFs. Similarities can be observed between the results of the two parts of this study (Figures 1–6), i.e., in both cases, the minimum fluidization velocity and the bubble size growth rate with the superficial gas velocity in the bubbling regime increased with IPFs while the average in-bed differential pressure drop in the bubbling regime decreased with IPFs. The polymer coating approach is therefore capable of simulating the conditions of a high temperature fluidized bed operated under the influence of IPFs at near-ambient conditions. The agglomeration phenomenon happening in high temperature cohesive beds, however, would not be mimicked by this approach since the reptation time of the PMMA/PEA polymer is longer than the idle time of the process. The idle time, which is the time that particles spend in the emulsion phase, represents the effective contact period for the agglomeration process to advance in the bed and is longer than the agglomeration time. Please click Additional Files below to see the full abstract

Fluidization of cohesive nanoparticles with a new pulsation technique

The nanoparticles are building block of many advanced materials that are developed for a variety of industries. Fluidization of the nanoparticles can improve dramatically quality of the final material in processes such as coating, drying and crystallization because of enhanced mixing conductions in a fluidized bed. However, due to severe presence of interparticle forces, the nanoparticles are very cohesive, and thus their fluidization is impossible with conventional methods. Authors developed a novel pulsation-assisted technic to effectively fluidize the nanoparticles of different types. The developed fluidization technic was primarily investigated inside a transparent tube with 2.5 cm diameter and 20 cm height. A solenoid valve was located in the reactor outlet to switch between ON and OFF positions to intermittently pressurize the gas inside the reactor and then let it exit. Two differential pressure transducers and a high-speed camera recorded the pressure fluctuations of the bed. Superficial gas velocity and intermittence frequency of the solenoid valve were varied to investigate fluidization quality. An experimental procedure was developed to estimate the maximum amount of interparticle forces between the nanoparticles in the bed. Investigations showed under optimum conditions when the solenoid valve was open an upward lift force was generated that helped fluidize the bed. The lift force was greater than sum of the bed weight and the maximum interparticle forces minus the drag force. Bed fluctuations were examined at temperatures 650, 700 and 750 °C, and it was revealed that the developed technique could be optimized to work at such temperatures