Reversed combustion of waste in a grate furnace - an experimental study

Most widely used concept for municipal solid waste (MSW) incineration is combustion on a moving grate with energy recovery. In MSW incinerators fresh waste stacked on a grate enters the combustion chamber, heats up by radiation from the flame above the layer and ignition occurs. Ignition front propagates downwards producing heat for drying and devolatilisation of the fresh waste below until it reaches the grate. The present project is investigating the so called reversed combustion of waste on a grate. In this new concept the fuel layer is ignited by means of preheated air from below without any external ignition source. As a result a combustion front will be formed close to the grate and will propagate upwards. In order to investigate reversed combustion an experimental set-up that is able to simulate a real moving grate furnace is designed. Experimental study was conducted to determine the influence of different factors (amount of primary air, fuel moisture content etc.) on process parameters. In this paper, the detailed description of setup, as well as the results from experiments will be presented

Computational fluid dynamic model for glycerol gasification in supercritical water in a tee junction shaped cylindrical reactor

Gasification in supercritical water is a very promising technology to process wet biomass into a valuable gas. Providing insight of the process behavior is therefore very important. In this research a computational fluid dynamic model is developed to investigate glycerol gasification in supercritical water, which takes place in a cylindrical reactor with a tee junction. The performance of the developed model is validated against experiment, and it shows that the model is able to describe the process very well. The experimental validation shows that the model slightly overestimates the outlet temperature on average by 6% and underestimates the carbon gasification efficiency on average by 16%. The flow behavior in the supercritical water gasification process is successfully described and a sensitivity analysis is conducted. It is revealed that the flow pattern of the process is heavily influenced by gravitational forces which significantly influences mixing and heat transfer

Low temperature water vapor pressure swing for the regeneration of adsorbents for CO₂ enrichment in greenhouses via direct air capture

CO2 enrichment in greenhouses can be achieved by extracting CO2 from the outside air. For this purpose, adsorbents based on Na2CO3 or K2CO3 are promising for trapping and releasing atmospheric CO2. Even though the CO2 capture by these adsorbents has been studied before, there is not much information about their regeneration at low temperatures and using air as flushing gas. In this work an experimental design study has been performed to understand the effect of temperature, water vapor pressure and air flow rate on CO2 desorption. The results show that K-based adsorbents are a more attractive option given their higher CO2 capture capacity and lower energy consumption compared to the Na-based ones. The estimated amount of K-based adsorbent with a capture capacity of 0.1 mmol CO2/gads and regenerated at 50 °C with 90 mbar H2O would occupy only 2% of the total volume contained in a closed greenhouse, fulfilling its daily CO2 demand

Catalytic upgrading of biomass pyrolysis vapours using Faujasite zeolite catalysts

Bio-oil produced via fast pyrolysis of biomass has the potential to be processed in a FCC (fluid catalytic cracking) unit to generate liquid fuel. However, this oil requires a significant upgrade to become an acceptable feedstock for refinery plants due to its high oxygen content. One promising route to improve the quality of bio-oil is to pyrolyse the parent biomass in the presence of a catalyst. This work investigates the influence of faujasite catalysts on the pyrolysis of pinewood. Pyrolysis process with Na-faujasite, Na0.2H0.8-faujasite, and H-faujasite (Na-FAU, Na0.2H0.8-FAU, and H-FAU) were carried out in a fixed-bed reactor at 500 °C. It is shown that, in the same condition, catalytic upgrading of pyrolysis vapour is superior to in-situ catalytic pyrolysis of biomass when it comes to quality of bio-oil. The yields of coke, gas and water increase while that of organic phase decreases proportional with the concentration of protons in catalysts. Compared to the other two catalysts, Na0.2H0.8-FAU removes the most oxygen from bio-oil, reduces amount of acids and aldehydes/ketones which result in a higher energy-contained and more stable oil with less corrosive property. However, the biggest contribution to the oxygen removal is via the formation of reaction water, which is not an optimum path. This leaves space for future development

Pyrolysis oil utilization in 50KWE gas turbine

The concept of using pyrolysis oil (PO) derived from biomass via a fast pyrolysis route for power and heat generation encounters problems due to an incompatibility between properties (physical and chemical) of bio-oil and gas turbines designed for fossil fuels. An extensive research has been performed on the production and improvement of pyrolysis oil but only few investigations were carried out on its utilization. The latter have shown a major difference in behavior of pyrolysis oil compared to fossil fuels during combustion processes. In this work, pyrolysis oil is co-fired with diesel in a 50 kWe gas turbine operating in idle mode. Stable mixtures with up to 20 wt.% of pyrolysis oil and diesel fuel were produced with utilization of a surfactant agent. To prevent feeding line deterioration due to acidic character of pyrolysis oil, a stainless steel nozzle was employed. Furthermore, the fuel emulsion was preheated up to maximum temperature of 80 oC in order to reduce the effect of high viscosity on the atomization process. Diesel distillate #2 was used as a reference fuel for a comparison of gas turbine performance and emissions with various PO content in the blends. During the combustion investigations, the amount of pyrolysis oil was gradually increased with simultaneous decrease of preheating temperature. In all investigated cases, the gas turbine was running stable at its maximum rotational speed (RPM). The CO level resulting from the study with different blends was generally slightly higher in relation to the diesel distillate fuel. NO emissions were in the range of few ppm and almost no detectable with common gas analyzing equipment. After a few hours of continuous operation, there were no signs of deterioration or contaminations inside the combustor. The study shows that pyrolysis oil gradually can be introduced in the market of fossil fuels and benefit to green power generation

Numerical modeling of self-heating and self-ignition in a packed-bed of biomass using XDEM

In a packed bed of biomass, spontaneous ignition might occur due to oxidation of volatiles and causes a serious and unforeseen risk. On the other hand self-ignition may be useful in gasifiers and combustors if it occurs at the expected location and time. Therefore self-ignition can be categorized as a favorable or an unfavorable process, which can be controlled by managing some parameters such as gas velocity and temperature. However, spontaneous ignition originates from a complex combination of physiochemical processes such as gas flow through the void space of the bed, heat and mass transfer between two phases, drying, devolatilization, gas phase reaction and char combustion and gasification. The main aim of this work is to investigate the characteristics of self-heating and self-ignition in a packed bed using XDEM as an Euler–Lagrange model. The influence of different parameters such as gas velocity, gas temperature, particle size and moisture content will be studied and discussed in details. The numerical model is validated with experimental data. Good agreements were achieved between predicted results and measurements. The results show that ignition delay increases with fuel properties such as moisture content and particle size, while it decreases with process conditions such as gas velocity and temperature. However ignition height shows an increase with gas velocity and a decrease with gas temperature and moisture content

Recycling Strategy for Bioaqueous Phase via Catalytic Wet Air Oxidation to Biobased Acetic Acid Solution

The bioaqueous phase generated during biomass conversion to biofuel and biochemicals, e.g., fast pyrolysis and ex situ catalytic pyrolysis, contains a large number of organics, leading to a high chemical oxygen demand (COD) for its treatment. In this study, we demonstrate its catalytic conversion to bioacetic acid solution and propose a recycling strategy thereof. We found that the diluted bioaqueous phase (e.g., C content 90%) converted to acetic acid with nondetectable impurities in solution. The solution contains 1.3-1.5 wt % acetic acid and can be directly used for demineralization of biomass in the biorefineries. This recycling strategy enhances the sustainability of the biobased economy and sheds light on production of biobased acetic acid, which has been recognized as a smart drop-in chemical