Hydrothermal Drying Research Articles

Changes in physicochemical properties of brown coal under hydrothermal modification

Hydrothermal drying of low-grade coals was first suggested in Austria as early as in 1920, when it envisaged treatment of a lump coal with 180–240 °C steam in an autoclave. Hydrothermal treatment (HTT) of brown high-ash coals at 200 to 250 °C causes certain changes in their structure and physicochemical properties, similar to those under low-temperature pyrolysis. Moreover, these changes occur at values 50–100 °C below the pyrolysis temperatures, and the HTT product is close to semi-coke in terms of its calorific value. During hydrothermal treatment, the surface of the coal phase becomes more hydrophobic, while the specific surface of the mineral fraction decreases and the swellability is lost, which leads to lower adsorption activity. Taken in combination, these effects significantly modify the processing properties of coal. When only brown coal-water separation is required, the HTT may be performed without adding free water; when changes the processing properties of coals are necessary, it is advisable to carry out hydrothermal treatment in suspensions containing approximately 50 % of free water. This treatment not only causes the removal of moisture, but also leads to certain other changes in the coal structure. The study was supported by a grant from the Russian Science Foundation (project No. 18-17-00169).

Development of sorption materials based on iron(III)-chloride-modified graphene oxide for selective removal of organic pollutants from aquatic media

The present work is aimed at developing an effective graphene-based sorbent for liquid-phase sorption of organic pollutants from aquatic media. The material synthesized in accordance with the method proposed represents a nanostructured composite possessing the hydrogel properties: structured three-dimensional carbon framework surface-modified with iron nanoparticles (i.e., graphene oxide (GO)/Fe-H2O). Moreover, the proportion of dry matter in the hydrogel was revealed by drying to a constant weight at a given temperature (110 °C), and the powdery form (GO/Fe-110) of the composite was obtained. Besides, the aerogel (GO/Fe-250) of the composite developed was formed, for which the hydrogel synthesized was subjected to hydrothermal drying in isopropanol for 6 h under supercritical conditions. The morphological, structural and porous characteristics of all these materials were determined. The sorption capacity of the nanocomposites was estimated for the removal (under dynamic conditions) of the synthetic organic dye, methylene blue, used as a target pollutant. The results of the studies showed that the maximum sorption capacity of the GO/Fe-H2O, GO/Fe-110 and GO/Fe-250 are ∼2500, ∼1500 and ∼2300 mg g−1, respectively. Besides, the high rate of the target pollutant removal from the aquatic media is a distinctive feature of the composites developed herein.

The effect of operation parameters on the hydrothermal drying treatment

The study was conducted to determine the effect of sewage sludge components on hydrothermal drying using the sludge of various wastewater treatment plants. According to the tests of equivalent reaction temperature and reaction time the moisture content of sludge can reduce to less than 60%. The solubilization ratio of BJ-Sample, HS-Sample1 and HS-Sample2 at reaction temperature of 190 °C were 5.32%, 6.58%, and 10.44%, respectively. There were still about 90% of the materials in the solid phase. It can be said that the characteristics of sludge had no effect on the hydrothermal drying. Thus this showed that hydrothermal drying technology was feasible for the treatment of sewage sludge. The volatile matter and fixed carbon was decreased after hydrothermal treatment, but the ash was increased. It was also observed that with the temperature rising, the volatile matter and fixed carbon were increased gradually and the ash was increased gradually as well. The natural drying characteristics of sludge product were monitored at the same time. From the results we can see that after 24 h the moisture content of sludge was reduced to less than 20%. 0–24 h was the rapid evaporation stage, 24–48 h was slow evaporation stage. The evaporation rate was 4.4 times higher than the untreated sludge samples in the rapid stage. Three different sludge natural drying tests showed that despite the different sludge samples, the results were the same. The optimum reaction temperature and time are 190 °C and 30 min respectively.

Study on the hydrothermal drying technology of sewage sludge

Drying of sewage sludge is an effective way for treatment and utilization of sewage sludge, where reduction of energy consumption is one of the major technical challenges. So we experimentally investigated the possibility of the hydrothermal treatment. We have found that treatment of sewage sludge by saturated steam with the temperature of 190°C and pressure of 20 bar can dramatically improve the dehydration performance of the slurry like product. And the water content can be reduced down to about 55% by a mechanical dehydration. After natural drying 24 h it can be reduced down to about 20%. The final product is almost odorless and can easily be used for the refuse derived fuel (RDF). The sewage sludge product may be used as land-fill, or burned in a boiler or incinerator.

Characterization of hydrothermally dried low-rank coals

Over a period of eight years (1989 through 1997) the Mineral Industry Research Laboratory (MIRL) at the University of Alaska, Fairbanks, AK, has investigated the effects of temperature, residence time and particle size on the degree of low-rank coal (LRC) upgrading for a nonevaporative, hydrothermal drying process, also known as hot water drying (HWD). The following three Alaskan LRC s were used in this study: Usibelli coal (Seam No. 4) from the Nenana Coal Field, Little Tonzona coal from near McGrath, and Beluga coal from the Beluga-Yentna field on the west side of Cook Inlet. Replicated factorial tests were conducted. Experimental results indicate that most of the low-rank coal upgrading via HWD occurs rapidly within the first 10 to 20 min of residence time. Thereafter, the upgrading process slows down, and more than 100 min of additional residence time is required to produce percentage increases equivalent to what was achieved in the first 10 to 20 min. The properties of the hot water dried products were very sensitive to process temperature. Calorific value, carbon and oxygen contents, equilibrium moisture levels and Hardgrove gindabilities all appear to change linearly with temperature within the 275 °C to 325°C (525°F to 615°F) range.

97/03553 Pipeline transportation of upgraded Yugoslavian lignite fuels

Hydraulic transport and handling procedures for coal are not widely used, but when practiced, they result in a technically and economically successful operation. Potentially the most attractive way to utilize lignitic coals for power generation would be to combine hydraulic mining techniques with aqueous ash removal, hydrothermal processing, solids concentration, and coal-water fuel (CWF) combustion. Technical and economic assessment of this operation is being implemented within the Yugoslavian-American Scientific Technical Cooperation Agreement. The Energy and Environmental Research Center (EERC), Grand Forks, North Dakota, with support from the U.S. Department of Energy, has entered into a jointly sponsored research project with Electric Power of Serbia (EPS), Belgrade, Yugoslavia, to investigate the application of the nonevaporative hydrothermal drying procedure, commonly called hot-water drying (HWD), developed at the EERC, to the lignite from the Kovin deposit. Advances in hydrothermal treatment of low-rank coals (LRCs) at the EERC have enabled cheaper, more reactive LRCs to be used in coal-water fuels (CWFs). HWD is a high-temperature, nonevaporative drying technique carried out at high pressure in water that permanently alters the structure of LRC. It solves the stability problems by producing a safe, easily transported, liquid fuel that can be handled and used like oil. Formore » continued or increased success, it is necessary to evaluate carefully all aspects of slurry technology that permit further optimization. This paper discusses some aspects of low-rank coal hydraulic transport combined with hydrothermal treatment as an alternative energy solution toward less oil dependence in Yugoslavia.« less

Overview of Low-Rank Coal (LRC) Drying

Low-rank coal (LRC) drying processes are generally categorized by operating temperature, drying environment, and type of feed or product. Within these broad categories, drying processes differ further according to the type of drying equipment and methods of quenching and stabilizing dried products. This paper focuses on the issue of the quality of products produced from a number of LRC drying processes that are commercial or have been demonstrated at a pilot-scale, including low and high temperature evaporative drying and non-evaporative processes, such as hydrothermal drying. Evaporative processes are usually the lowest cost and are preferred when the dried product is used immediately. This avoids the problems of moisture reabsorption, dust generation and spontaneous combustion associated with LRC transportation and long term storage. Hydrothermal drying followed by. low-rank coal-water fuel production is one of the most promising techniques for eliminating stability problems, while producing a value added fuel that will compete in the heavy oil market, not the steam coal market.

Dehydration of Alaska’s low-rank coals by hydrothermal treatment

The combination of high moisture and low heating value has restricted most low-rank coal (LRC) usage worldwide to mine-mouth power generation. The objective of this study was to subject two Alaska low-rank coals to hydrothermal drying to enhance their marketability in the Pacific Rim markets and to evaluate the chemical and physical properties of the dried products as a function of process conditions.