Yongfa Zhang

Pyrolysis characteristics of macerals separated from a single coal and their artificial mixture

Abstract Sufficient quantities of the three major maceral groups (vitrinites, fusinites and liptinites) were separated from a single coal, Pingshuo bituminous coal. Nine model coals were prepared by mixing the individual macerals in different amounts. The behaviour and kinetics of these 12 samples during nitrogen pyrolysis have been investigated and the pyrolysis mechanism has been analysed in conjunction with the information obtained by Fourier transform infrared spectrometry and X-ray diffraction. The data presented indicate that there are three stages in the overall devolatilization process, and each stage is a first-order reaction. The pyrolysis conversion of the maceral mixtures (model coals) is equal to a calculated sum of the individual macerals, and the activation energy in each stage equals the sum of the activation energies of the individual macerals.

Resource treatment of HPF coking desulphurisation waste solution: composition and characteristics of pyrolysis

HPF (H: hydroquinone; P: dinuclear cobalt-phthalocyanine sulfonate; F: ferrous sulphate) coking desulphurisation waste solution (CDWS) produced from coking oven gas desulphurisation process is an extremely harmful pollutant. The fundamental natures of this solution, which involves its main ingredient and content, type of organic matter, thermal decomposition characteristics of salt, and relationship of boiling point and density with salt content, were examined in this paper. Results show that inorganic salts in CDWS mainly contain ammonium thiosulfate and ammonium thiocyanate; the content and ratio of this two differ with factories and batches of CDWS. Organic matters in CDWS mainly contain phenolic and nitrogenous organic compounds, which together account for 98.79% of the total organic matter. The salts in CDWS are of poor thermal stability and can be decomposed at 425°C. The density and boiling point of CDWS increase with increasing salt content. Heating temperature should be strictly controlled, and solution flow should be supplemented by stirring at vacuum conditions during concentration and drying.

Study on the pyrolysis treatment of HPF desulfurization wastewater using high-temperature waste heat from the raw gas from a coke oven riser

Thermogravimetric TG and a single riser from an industrial 4.3 m coke oven were used as pyrolysis reactors to systematically study the newly developed pyrolysis treatment of desulfurization wastewater. The TG study showed that the mixed salt in the desulfurization wastewater was transformed into the crystalline form of ammonium thiocyanate (in the temperature range 95.87–127.38 °C), followed by the isomerization of ammonium thiocyanate to thiourea (in the temperature range 127.38–246.26 °C), involving a total of five major stages. The final pyrolysis temperature was 540 °C, and the cumulative weight loss was 99.57%. The study on the single riser from an industrial 4.3 m coke oven showed that the relationship between the spray amount of desulfurization wastewater (v), the temperature drop (ΔT) and the concentration of ammonium thiocyanate (c) in the coke-oven raw gas at the outlet of the rising pipe were respectively ΔT = −2.939v and c = f(v). The maximum desulfurization wastewater treatment capacity of the 4.3 m single riser was 61.98 kg h−1. The spraying optimization conditions were: spraying position, 3 m from the water seal cap of the riser; spraying amount, 50–55 L h−1; spraying time, from 10 min after the coal loading to less than 20 h during the coking process. An industrial test device for treating 12 000 tons of desulfurization wastewater was constructed, which then ran normally, with the new technology for treating the high concentration polluted wastewater–desulfurization wastewater formed.

Preparation of High-Strength Gasified Coke Used for DRI from Low Rank Coal

This paper describes attempts to produce high-strength gasified coke for the production of direct reduced iron (DRI) from low rank coal. The method involves combining modified lignite with original low rank bituminous coal, briquetting and then carbonizing. The effects of content of modified coal and carbonization temperature on the qualities of coke were investigated. The results showed that the change of carbonization yield and density of coke was not obvious with the variety of modified coal content from 0 to 20%. The compressive strength of coke ascended with the increase of proportion of the modified coal. The yield of carbonization decreased gradually with temperature increased from 350 °C to 850 °C, and the compressive strength and density of coke showed a trend of decreasing firstly and then increasing. The resulting carbonized briquettes had a compressive strength as high as 2.05 ~ 9.10 MPa and density of 0.87 ~ 0.96 g/cm3. The process of preparated gasified coke from low rank coal, its not only realized the low rank coal clean efficient utilization, but also had a significant economic benefit from Heat - Electricity and Metallurgy coproduction.

Gas heat carrier pyrolysis of low rank coal and associated heat transfer characteristics

A small scale gas heat carrier pyrolysis fixed-reactor (6–9 kg h−1) was established. The pyrolysis temperature and residence time effect the dehydration process, pyrolysis products, caking property, and temperature profile characteristic. The dehydration process is completed below 300 °C. High temperature and short transfer distance shorten the pyrolysis time. With an increase in the final pyrolysis temperature, the yield of the volatiles and tar increases; however, that of the char decreases. The residence time significantly influences the char yield at 460 °C. The coal begins to agglomerate after 25 min at 460 °C for the first time. Agglomeration of the coal particles increases with an increase in the pyrolysis temperature and residence time. Based on the temperature profile, the temperature curve in the coking chamber can be divided into three stages: the rapid temperature-decline, coal temperature-increase stage, and coal temperature constant stage. The temperature of coal and gas achieves a short relative balance, which causes the temperature turning point between the first two stages. The exothermic heat makes the final temperature of coal higher than that of the inlet gas, thus the exothermic reaction cannot be ignored.