Evaluating the manufacturability and combustion behaviors of sludge-derived fuel briquettes

Based on the physical and chemical properties as well as calorific values of pulp sludge and textile sludge, this study investigates the differences between manufacturability, relationship between extrusion pressure and formability, as well as stability and combustion behaviors of extruded sludge-derived fuel briquettes (ESBB) and cemented sludge-derived fuel blocks (CSBB). The optimum proportion and relevant usage ESBB policies are proposed as well. Experimental results indicate that a large amount of water can be saved during the ESBB manufacturing process. Additionally, energy consumption decreases during the drying process. ESBB also has a more compact structure than that of CSBB, and its mean penetration loading is approximately 18.7 times higher as well. Moreover, the flame temperature of ESBB (624–968 °C) is significantly higher than that of CSBB (393–517 °C). Also, the dry bulk density and moisture regain of ESBB is significantly related to the penetration loading. Furthermore, the optimum mix proportion of ESBB is co-determined by the formability of pulp sludge and the calorific values of textile sludge. While considering the specific conditions (including formability, stability and calorific values), the recommended mix proportion for ESBB is PS50TS50.     

Effect of pressure and atmosphere during hydrothermal treatment on the properties of sewage sludge-derived solid fuel

Journal of Material Cycles and Waste Management - Efforts to improve the performance of hydrothermal treatment (HT) in producing high-quality solid fuel from sewage sludge were carried out by...     

Modeling of the reburning process using sewage sludge-derived syngas

Gasification of sewage sludge can provide clean and effective reburning fuel for combustion applications. The motivation of this work was to define the reburning potential of the sewage sludge gasification gas (syngas). A numerical simulation of the co-combustion process of syngas in a hard coal-fired boiler was done. All calculations were performed using the Chemkin programme and a plug-flow reactor model was used. The calculations were modelled using the GRI-Mech 2.11 mechanism. The highest conversions for nitric oxide (NO) were obtained at temperatures of approximately 1000-1200 K. The combustion of hard coal with sewage sludge-derived syngas reduces NO emissions. The highest reduction efficiency (>90%) was achieved when the molar flow ratio of the syngas was 15%. Calculations show that the analysed syngas can provide better results than advanced reburning (connected with ammonia injection), which is more complicated process.     

Analysis of the combustion and pyrolysis of dried sewage sludge by TGA and MS

In this study, the combustion and pyrolysis processes of three sewage sludge were investigated. The sewage sludge came from three wastewater treatment plants.Proximate and ultimate analyses were performed. The thermal behaviour of studied sewage sludge was investigated by thermogravimetric analysis with mass spectrometry (TGA-MS). The samples were heated from ambient temperature to 800 °C at a constant rate 10 °C/min in air (combustion process) and argon flows (pyrolysis process). The thermal profiles presented in form of TG/DTG curves were comparable for studied sludges. All TG/DTG curves were divided into three stages. The main decomposition of sewage sludge during the combustion process took place in the range 180–580 °C with c.a. 70% mass loss. The pyrolysis process occurred in lower temperature but with less mass loss. The evolved gaseous products (H₂, CH₄, CO₂, H₂O) from the decomposition of sewage sludge were identified on-line.     

Influence of combustion temperature on the performance of sewage sludge ash as a supplementary cementitious material

The potential for using sewage sludge ash (SSA) as a supplementary cementitious material (SCM) has been investigated. Controlled combustion of sewage sludge collected in Croatia from two wastewater treatment plants produced SSA with different characteristics. These were used to substitute for cement in mortar samples. The chemical composition and physical properties of SSA depend on wastewater composition, the sludge treatment process and the combustion temperature. These factors influence the suitability of SSA to be used as a SCM. For three different combustion temperatures (800, 900 and 1000 °C), it was concluded that properties of fresh mortar were not affected while in the hardened state, the most favorable combustion temperature is 900 °C regarding mechanical properties. Regardless of combustion temperature, for all types of SSA used in mortars as cement replacement (up to 30%), the average decrease in both compressive and flexural strength values was less than 8% for every 10% of added SSA. The results presented indicate that using up to 20% replacement of cement by SSA produces mortars that meet the specific technical requirements analyzed in this work.     

一项降低电厂Nox排放量的技术

对某厂现有锅炉的燃烧调整试验表明，针对不同的锅炉和煤种，通过调整锅炉运行的过剩空气系数或改变二次风配风方式，可达到降低NOx排放量的目的。     

Decreased PCDD/F formation when co-firing a waste fuel and biomass in a CFB boiler by addition of sulphates or municipal sewage sludge

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are formed during waste incineration and in waste-to-energy boilers. Incomplete combustion, too short residence times at low combustion temperatures (<700 °C), incineration of electronic waste and plastic waste containing chlorine are all factors influencing the formation of PCDD/Fs in boilers. The impact of chlorine and catalysing metals (such as copper and iron) in the fuel on PCDD/F formation was studied in a 12 MW_th circulating fluidised bed (CFB) boiler. The PCDD/F concentrations in the raw gas after the convection pass of the boiler and in the fly ashes were compared. The fuel types were a so-called clean biomass with low content of chlorine, biomass with enhanced content of chlorine from supply of PVC, and solid recovered fuel (SRF) which is a waste fuel containing higher concentrations of both chlorine, and catalysing metals. The PCDD/F formation increased for the biomass with enhanced chlorine content and it was significantly reduced in the raw gas as well as in the fly ashes by injection of ammonium sulphate. A link, the alkali chloride track, is demonstrated between the level of alkali chlorides in the gas phase, the chlorine content in the deposits in the convection pass and finally the PCDD/F formation. The formation of PCDD/Fs was also significantly reduced during co-combustion of SRF with municipal sewage sludge (MSS) compared to when SRF was fired without MSS as additional fuel.     

Tar-free fuel gas production from high temperature pyrolysis of sewage sludge

Pyrolysis of sewage sludge was studied in a free-fall reactor at 1000–1400 °C. The results showed that the volatile matter in the sludge could be completely released to gaseous product at 1300 °C. The high temperature was in favor of H₂ and CO in the produced gas. However, the low heating value (LHV) of the gas decreased from 15.68 MJ/N m³ to 9.10 MJ/N m³ with temperature increasing from 1000 °C to 1400 °C. The obtained residual solid was characterized by high ash content. The energy balance indicated that the most heating value in the sludge was in the gaseous product.     

Novel fry-drying method for the treatment of sewage sludge

The purpose of this study is to introduce an efficient drying method named “fry-drying technology” for the treatment of sewage sludge. The basic principle of this method lies in the rapid escape of moisture from sludge material through its pores into the oil medium driven by the strong pressure gradient formed between sludge and oil media. This beneficial pressure distribution for moisture transfer can be established by the subtle combination of the difference of physical properties of specific heat and boiling temperature between water and oil. In order to determine the physical characteristics of this fry-drying technology, a series of experiments were performed in which important parameters, such as heating oil temperature, drying time, oil type, and sludge size, were varied. Numerical calculations using a single solid spherical particle model without any porosity were used to resolve the particle size effect associated with sludge drying.     

燃料分级燃烧最佳风煤配比的数值模拟

运用Fluent软件对某电厂1160t／h锅炉的燃烧过程和NOx生成特性进行数值模拟。通过调节风煤配比来改变燃烧区域风粉的混合以及燃烧区内的气氛，得到炉内C（s）、CO2、CO、O2、H2O（g）的浓度分布和NOx生成特性。对于煤粉的燃烧特性而言，NOx的来源依赖于煤中氮的析出和氧化。从模拟结果可以看出，煤量变化率直接影响燃烧生成物在锅炉中的分布，从而影响NOx排放浓度。随着煤量变化率的增大，NOx的排放浓度先减少后增加，即燃料分级工况存在最佳风煤配比。从所计算工况的结果比较，得出了最佳风煤配比。     

Mathematical modelling of sewage sludge incineration in a bubbling fluidised bed with special consideration for thermally-thick fuel particles

Fluidised bed combustor (FBC) is one of the key technologies for sewage sludge incineration. In this paper, a mathematical model is developed for the simulation of a large-scale sewage sludge incineration plant. The model assumes the bed consisting of a fast-gas phase, an emulsion phase and a fuel particle phase with specific consideration for thermally-thick fuel particles. The model further improves over previous works by taking into account throughflow inside the bubbles as well as the floating and random movement of the fuel particles inside the bed. Validation against both previous lab-scale experiments and operational data of a large-scale industrial plant was made. Calculation results indicate that combustion split between the bed and the freeboard can range from 60/40 to 90/10 depending on the fuel particle distribution across the bed height under the specific conditions. The bed performance is heavily affected by the variation in sludge moisture level. The response time to variation in feeding rate is different for different parameters, from 6min for outlet H(2)O, 10min for O(2), to 34min for bed temperature.     

Study on the co-combustion process and mercury emission characteristics of sewage sludge-coal slime coupled fuel

Journal of Material Cycles and Waste Management - To realize the clean and efficient resource utilization of sewage sludge (SS) and coal slime (CS), single-component and coupled fuels were...     

A new method for evaluating the sewage sludge pyrolysis kinetics

A new method to simplify calculation the kinetics model is applied to sewage sludge pyrolysis based on the assumption that volatile run out as soon as it formed and during temperature arising process in this study. Difference method widely used to solve math problems is conducted to calculate kinetics parameters. Pyrolysis experiments are carried out at heating rates of 10, 15, 20, and 50 °C/min. All the TG curves are divided into three parts which are beginning decomposition temperature range, main decomposition temperature range, and final decomposition temperature range. The second one is employed to determine the parameters for more than 70% of the total mass loss occurs in this range. According to the developed method, the react order, reaction energy and pre-exponential factor are obtained, which are in the range of 3.9–4.1, 82.3–109.2 kJ/mol and 7.7 × 10⁶–2.8 × 10⁹/min, respectively, which are in the range of that reported previously. As a comparison experimental data with calculated data, the well fitting results indicate that this method is appropriate for simulating sludge pyrolysis kinetics.     

污泥灰中磷的湿化学法回收技术研究进展

从污泥灰中磷的提取、磷与重金属的分离和磷产品的制备3方面综述了国内外湿化学法回收污泥灰中磷的研究进展,重点分析了磷提取过程中的各种影响因素,并对今后污泥灰中磷的湿化学法回收技术的研究方向进行了展望。指出:利用萃取的方法将提取液中的无机强酸萃取出来并回收重复利用,可大幅降低酸的消耗量;在回收磷的同时可研究回收不同种类金属的方法,尤其是价值较大的重金属,以进一步提高污泥灰资源的回收价值。     

污水处理固体废弃物污泥的处置方法研究

从生活污水处理工艺出发介绍污泥产生的环节,探究污泥传统处置方法和资源化处置方法,同时对污泥源头减量化方法做了详细论述,最后分析了污泥处置成本的影响因素,对污泥环保处置提供参考与帮助.     

石灰石-石膏法烟气脱硫系统处理废稀硫酸

采用石灰石-石膏法脱硫装置处理废稀硫酸.研究了石灰石浆液和废稀硫酸的不同投加顺序以及不同反应晶种(石膏浆液、石膏稀浆液)对所得石膏晶粒形态和抽滤物含水率的影响.试验结果表明:与废稀硫酸加入石灰石浆液的方式相比,石灰石浆液加入废稀硫酸的方式更利于石膏结晶,晶粒更大,所得石膏抽滤物含水率更低;以石膏浆液和石膏稀浆液作为反应...     

Evaluation on the property of sewage sludge cake by thermal treatment

The sewage sludge cake (SSC) used in this study was provided by a K-wastewater treatment plant in Kyonggi-Do, Korea. The characteristics of the SSC, such as particle size, water content, and composition were analyzed. Both the Korea extraction test (KET) and the toxicity characteristic leaching procedure (TCLP) were used to estimate whether the SSC was hazardous. In thermal experiments, the temperature was varied in the range 400° to 900°C and the heating time was varied from 1 to 6 h. The effects of thermal treatment temperature and time were evaluated by turbidity tests on the resultant SSC. On a dry basis, SSC mainly consisted of combustible content (60.2%) and phosphorous (25.9%). The turbidity of SSC was initially estimated in terms of the sedimentation time. The turbidity of SSC decreased exponentially from 9873 FAU at 0 h to 986 FAU at 6 h, so that the sedimentation time of SSC was established as 6 h. From the results of the thermal treatment at 600°C, thermal time can be determined by 2h because the turbidity of SSC is decreased dramatically within 1h and is stabilized after 2h. The turbidity of SSC decreased when the thermal treatment temperature increased from 400° to 900°C. The turbidity after thermal treatment at 400°C for 2 h was 29 FAU and this became almost 10 FAU at 600°C. The SSC was not hazardous, because KET and TCLP analysis produced values that were smaller than the regulatory levels. Hence, it was concluded that SSC can be stabilized by thermal treatment and can be used as a recycled material.     

Assessment of wood pellet combustion in a domestic stove

Wood pellet is a densified fuel with homogeneous physical properties suitable for use at various scales in domestic and industrial furnaces. A wood pellet stove is a small-scale furnace for domestic heat production that can replace conventional oil or gas boilers. Since the fuel properties of wood pellet are very different from those of oil or gas, the design of a wood pellet stove requires profound understanding of solid fuel combustion as well as of gas flow mixing and reactions. Due to limitations on the height of an installed furnace (~1 m), poor design of the furnace, air supply, fume extraction, or the heat exchanger may lead to excessive CO emissions or low energy efficiency. This study evaluated the design of an existing wood pellet stove with 30,000 kcal/h capacity, using experimental and computational techniques in order to optimize the furnace design. The results show that it is critical to minimize unused furnace volume and to enhance gaseous mixing for reduced CO emissions while maintaining sufficiently high temperatures for fast oxidation.