Houzhang Tan

Further study on biomass ash characteristics at elevated ashing temperatures: the evolution of K, Cl, S and the ash fusion characteristics.

Based on the ash-related problems during biomass combustion, the evolution of element S, Cl, K and chemical components and ash fusion characteristics of capsicum stalks, cotton stalks and wheat stalks ashed at 1000, 1200 and 1400 °C are further studied by XRF and XRD. Cl disappears at 815 °C in the form of HCl due to the aluminosilicate of sylvite. Above 1000 °C, inorganic S is released in the form of SO2 by the silicate of K2SO4, which is the main reason that ashing ratio decreases at high temperature. Except of the evaporation of KCl and K2SO4 aerosol which cause the release of K, Cl and S, K may be also reduced by the organic decomposition and the releases of metal K and KOH. The ash fusion characteristics of biomass are mainly dependent on the high-temperature molten material built up by quartz, potassium iron oxide and silicates.

Kinetics investigation on the reduction of NO using straw char based on physicochemical characterization

NO reduction using straw-char has been investigated in a fixed bed, and the effects of char-preparation temperature, reduction temperature, char concentration C(char) and NO concentration C(NO) were considered. Straw char was prepared at three temperatures, 873, 1073 and 1273K. The characterization was conducted by employing SEM-EDS, XRD, BET and TGA. Results show that the char prepared at 1073K holds the most developed pore structure and surface area, the best combustion activity, and the highest NO reduction rate. The reduction rate of NO linearly increases with increasing char concentration, but decreases with increasing NO concentration following a power-function relation. A transition temperature region from dynamic-control to diffusion-control is found to be around 1173K. In the dynamic-control region, the apparent activation energy E of char-NO reaction is in the range of 89.78-95.41kJ mol(-1), affected inconspicuously by the char-preparation temperature. The reaction rate between NO and straw-char is given by r(NO)=k(0)·exp(-11,069/T)·C(NO)(0.89)·C(char).

Investigation on the fast co-pyrolysis of sewage sludge with biomass and the combustion reactivity of residual char

Gaining the valuable fuels from sewage sludge is a promising method. In this work, the fast pyrolysis characteristics of sewage sludge (SS), wheat straw (WS) and their mixtures in different proportions were carried out in a drop-tube reactor. The combustion reactivity of the residual char obtained was investigated in a thermogravimetric analyzer (TGA). Results indicate that SS and WS at different pyrolysis temperatures yielded different characteristic gas compositions and product distributions. The co-pyrolysis of SS with WS showed that there existed a synergistic effect in terms of higher gas and bio-oil yields and lower char yield, especially at the WS adding percentage of 80wt%. The addition of WS to SS increased the carbon content in the SS char and improved char porous structures, resulting in an improvement in the combustion reactivity of the SS char. The research results can be used to promote co-utilization of sewage sludge and biomass.

Short Review on the Origin and Countermeasure of Biomass Slagging in Grate Furnace

Given the increasing demand for energy consumption, biomass has been more and more important as a new type of clean renewable energy source. Biomass direct firing is the most mature and promising utilization method to date, while it allows a timely solution to slagging problems. Alkali metal elements in the biomass fuel and the ash fusion behavior, as the two major origins contributing to slagging during biomass combustion, are analyzed in this paper. The slag presents various layered structures affected by the different compositions of ash particles. Besides, the high-temperature molten material which provides a supporting effect on the skeletal structure in biomass ash was proposed to evaluate the ash fusion characteristics. In addition, numerous solutions to biomass slagging, such as additives, fuel pretreatment and biomass co-firing, were also discussed.

A Mechanism Study on the Decomposition of Sulfate in Zhundong Coal with High Sulfur Content in Coal Ash

Sulfate in Zhundong (ZD) coal combustion plays a significant role in fouling, slagging, and particle emissions. This study aimed to investigate the effect of SiO2 and kaolin addition on sulfate transformation in ZD coal ash by using thermogravimetric analysis (TGA) and other characterizing methods for ash with SiO2 and kaolin addition under different temperatures. Results showed that SiO2 and kaolin both enhanced the decomposition of sulfates in ZD coal ash under higher temperatures. The decomposition of sulfates in pure ZD coal ash started above 1050 °C, while the starting temperature was ahead by 50 and 100 °C, when SiO2 and kaolin were added, respectively. Kaolin addition was more efficient to improve the thermal decomposition of sulfates than SiO2 addition. However, the enhanced effect of SiO2 and kaolin was very weak below 815 °C. The thermal calculation results also gave the similar result on the enhancement effect on sulfate decomposition of SiO2 and kaolin addition.

Prediction of Calorific Value of Coal Using Real Power Plant Data

With the depletion of coal in the world, coal quality fluctuates and deviates greatly from the designed coal in many large scale coal-fired power plants. This increases the coal consumption while reduces the boiler combustion efficiency and stability. Thus, it is very important to conduct real-time measurement to the quality of the coal for optimizing the operation. The calorific value analysis is a significant part of the coal quality analysis, and regular proximate analysis method can’t meet real-time control requirements. In this chapter, an artificial neural network (ANN) model using real plant data for prediction of net calorific value of coal in a China power plant is reported. A three-layer BP neural network has been adopted. The input parameters selection was optimized with a compromise between smaller number of parameters and higher level of accuracy through sensitivity analysis. The activation function selection was also discussed in details. The results indicate that when the pureline was selected as the activation function for hidden layer and logsig was selected as the activation function for output layer, the prediction is most accurate. The results have shown good potential for predicting the net calorific value of coal using the real time data. This information will enhance the performance of the combustion control system for power utilities.

Decision Making on Most Economical Coal for Coal-Fired Power Plants Under Fluctuating Coal Prices

A long-term (8 years) experimental investigation has been carried out to analyze the effect of coal quality on the economy of power plants and to develop a predictive method for the determination of the most economical coal in a fluctuating coal market. The research results show that the facility maintenance costs, the combustion-supporting oil consumption, and the frequency of tube explosion increase exponentially with the ash content increasing, and the total maintenance costs increase sharply when the quality of the coal declining significantly from the designed coal. Taken into considerations the coal-purchasing costs, facility maintenance costs, emission costs, etc., a comprehensive mathematical model has been developed to predict the most economical coal, which is the coal with an ash content of 28.9% for the power plant investigated. Finally, a rapid calculation method has been proposed to determine the most economical coal in a fluctuating coal price market.

The Promotion Mechanism of Silicon–Aluminum on the Decomposition of Sulfates in Biomass Ash

The Si–Al additives shared positive effects on relieving the severe problems of slagging, fouling, and depositions by destructing the alkali sulfates and chlorides during biomass combustion. In the present study, the decomposition of sulfates in the biomass ash was studied by using XRD, XRF, and TG-DSC. Results showed that sulfates in the biomass ashes began to decompose over 1000 °C and almost completely at 1100 °C. The aluminum–silicon additives promoted the decomposition of sulfates, but the Kaolin addition showed a stronger promotion effect. It was further proved by the further analysis of thermo-equilibrium calculation and TG-DSC on the biomass ash and potassium sulfate.

The Layered Structure of Ash Deposition in a 350 MW PC Furnace Burning High Sodium–Calcium Lignite

The high content of sodium and calcium in Xinjiang lignite induces severe slagging and ash deposition in pulverized coal furnaces. In the present study, kaolin was co-fired with high sodium–calcium lignite (HSCL) in a 350 MW PC furnace for 9 months to inhibit slagging and deposition, and the slags and deposits along the furnace were collected and analyzed by using EDS and XRD. The results showed that when average sodium content in ash was controlled below 2.1 %, there was no severe slagging observed. The slagging showed distinguishing structure and composition on different heating surfaces. In furnace chamber, slags grew windward because molten or soften ash moved with the tangential gas flow and adhered on the cooled water wall. In the lower temperature region below burners, amounts of sulfur and ferrum was found, indicating significant sulfate condensing and molten-salt corrosion; while in the water wall of higher temperature region around burners, no sulfate was found in slags which were porous and mainly contained aluminosilicates. A layered structure of ash deposition was observed on the heating surfaces of medium gas temperature below 1000 °C. Calcium sulfates were enriched in the bottom layer adhering on tube surfaces and should play an important role on the initial layer formation. With the growth of ash deposition, the surface temperature of ash layer remarkably increased and the capture of gaseous sodium by ash layer was significantly enhanced at such high temperatures, resulting in a higher sodium content of outer layer than that of inner layer.

Mitigation of Climate Change by Reducing Carbon Dioxide Emissions in Cement Industry

The cement industry is an energy intensive industry, and one of the largest carbon emitting industrial sectors. It is emitting 5 % of global anthropogenic carbon dioxide emissions, with especially high growth in Asia. While the energy efficiency of cement production has been increased significantly, the emissions can be further reduced by replacing conventional fossil fuels with alternative ones, mostly of waste origin. Due to the lower heating value of waste derived fuels than of the standardly used coal, the use of such fuels is possible where there is no need for very high process temperatures, e.g. in cement calciners where the desirable operating temperature is around 950 °C. Using waste derived fuels in cement calciners does not only reduce combustion related CO2 emissions in cement production by 10-30 %, depending on the amount of used waste derived fuels and the biogenic fraction in the used waste derived fuel, but is also an environmentally beneficial alternative to waste landfill disposal. However, incineration of high share of waste derived fuels in cement calciners still faces significant challenges. A possibility for the ex-ante control and investigation of the incineration process are Computational Fluid Dynamics - CFD simulations. Early comprehensive information, parametric studies and initial conclusions that can be gained from CFD simulations are very important in handling modern combustion units. The purpose of this paper is to present the benefit of using waste derived fuels in the cement industry, and to give some preliminary results on waste incineration numerical modelling.