Raw Lignite Research Articles

The effect of the calcium in lignite on its effectiveness as a reburn fuel

The effect of the calcium present in lignite on the effectiveness of NO reduction in the reburning method has been studied in the 900–1100 °C temperature range. Lignites from three Polish mines were used. The experiments were carried out in a laboratory scale drop-tube furnace reactor. The demineralised lignites were loaded with Ca using: calcium acetate Ca(CH 3COO) 2, calcium hydroxide Ca(OH) 2 and calcium carbonate CaCO 3. For the reburning process the catalytic effect of the presence of calcium in lignite was found to be rather modest (approx. ±20%) in the temperature range studied. It was shown that up to 1000 °C the calcium added to the demineralised lignites improved their effectiveness as reburn fuels. The effect was almost reversed when the reburn temperature was raised to 1100 °C. With the impregnated lignites the extent of NO reduction appeared to be practically independent of the calcium compound used. Mineral matter in raw lignite exerts a similar catalytic effect to calcium introduced by impregnation.

Determination of the optimal conditions for obtaining potassium nitro-humate from lignite

Raw lignite is enriched by humic acids by oxidation with nitric acid. The optimal conditions for producing potassium nitro-humate were defined by investigating the level of neutralization of the oxidized lignite, by means of potassium hydroxide. The increased content of humic acids and potassium in potassium nitro-humate makes it applicable as an organic-mineral fertilizer.

Decarboxylation of Beypazari Lignite by the Catalytic Effect of Cu2+, Zn2+, and Ag+ Ions

Decarboxylation of the Beypazari lignite with Cu2+, Zn2+, and Ag+ metal ions used as catalysts was investigated. Change in the calorific values after decarboxylation of the raw and demineralized coal with these metal ions was determined. Heating the raw and demineralized Beypazari lignite samples to temperatures between 100°C and 230°C for 10–60 min, the calorific values seemed to increase to about 10–20% higher values than those of the unheated samples. Heating the samples of Beypazari lignite charged with metal cations yielded products of higher calorific values than those of untreated lignite. The optimum metal concentration to obtain decarboxylated lignites with the highest calorific value for each metal-lignite group in the decarboxylation experiments were found as 4% Ag+, 3% Cu2+, and 1% Zn2+ for the raw lignite and 1% Ag+, 3% Cu2+, and 3% Zn2+ for the demineralized lignite. Addition of metals to the raw and demineralized samples decreased the activation energy of decarboxylation reactions. Cu2+ seemed to be the most effective catalyst by reducing the activation energy to about 7–8 kJ/mol both in the decarboxylation reactions of raw and demineralized lignite samples. 13C NMR measurements revealed that the aromaticity of the decarboxylated products of the raw lignite seemed to stay constant and those of demineralized lignite increased slightly. The sequence of the rate of loss of the oxygen functional groups in decarboxylation reactions for all of the metal charged sample was found to be carbonyl > carboxyl > carboxylate > hydroxyl. If the metal ions were compared in terms of effectiveness in decarboxylation reaction, the order was as follows: Cu2 > Ag > Zn2 (for raw lignite samples) and Cu2 > Zn2 > Ag (for demineralized lignite samples).

Microbial desulfurization of solubilized coal : Baek, K. et al. Bio-technology Letters, 2002, 24, (5), 401–405

The purpose of the present work was to investigate the effect of the concentration of HI and reaction time in the chemical desulfurization of Cayirhan lignite in a microwave energy set up and to compare the results with those obtained in a thermal heating system. As the concentration of the HI was increased, the extent of desulfurization was also increased in all the experiments done for all of the samples of lignite. The main difference between the thermal and microwave heating was the extremely short times for desulfurization in the case of microwave experiments. After desulfurization experiments Stotal/C ratio of all of the samples decreased to a lower value than that of the raw lignite which was 0.034. The loss of the sulfur containing bands in the FTIR spectra of the desulfurized lignite showed that the HI treatment was effective in the cleavage of dithioethers and thioetheric groups. Sulfur containing functionalities like thioethers and thiols although usually requiring strong reducing agents could be removed in significant amounts with concentrated hydroiodic acid from the coal matrix. The rapidity of the desulfurization reactions with microwave heating in concentrated HI was probably due to localized superheating which made HI more effective in the reactions such as with thioethers and thiols that normally resisted to cleavage by HI under thermal heating conditions.

Chemical desulfurization of Turkish Cayirhan lignite with HI using microwave and thermal energy ☆

The purpose of the present work was to investigate the effect of the concentration of HI and reaction time in the chemical desulfurization of Cayirhan lignite in a microwave energy set up and to compare the results with those obtained in a thermal heating system. As the concentration of the HI was increased, the extent of desulfurization was also increased in all the experiments done for all of the samples of lignite. The main difference between the thermal and microwave heating was the extremely short times for desulfurization in the case of microwave experiments. After desulfurization experiments S total/C ratio of all of the samples decreased to a lower value than that of the raw lignite which was 0.034. The loss of the sulfur containing bands in the FTIR spectra of the desulfurized lignite showed that the HI treatment was effective in the cleavage of dithioethers and thioetheric groups. Sulfur containing functionalities like thioethers and thiols although usually requiring strong reducing agents could be removed in significant amounts with concentrated hydroiodic acid from the coal matrix. The rapidity of the desulfurization reactions with microwave heating in concentrated HI was probably due to localized superheating which made HI more effective in the reactions such as with thioethers and thiols that normally resisted to cleavage by HI under thermal heating conditions.

Combined effects of pressure and ion-exchangeable metallic species on pyrolysis of Victorian lignite

A set of ion-exchanged samples prepared from Loy Yang lignite was pyrolyzed in a wire-mesh reactor at elevated pressures from 1 to 36 bar. The tar yields from the pyrolysis of H-form (acid-washed) sample at a fast heating rate of 1000 °C s −1 were drastically reduced by increasing pressure to 6 bar and then remained unchanged with further increase in pressure to 36 bar. This behavior of the tar yield was in sharp contrast to that from the raw lignite which showed a minimum with increasing pressure. The sensitivities of the tar yields to changes in the heating rate were also suppressed by increasing pressure. The tar yields from Ca-form and Na-form samples (prepared by ion-exchanging Ca and Na on the H-form sample, respectively) were not very sensitive to changes in the heating rate and pressure up to 11 bar. At 20 bar, the tar yields from the Na-from sample nearly doubled whereas from the Ca-form sample nearly halved compared to those respective values at 1 bar. Although increasing pressure is thought to cause changes in the intra-particle mass transfer processes of volatile precursors, the rate of formation of volatile precursors tends to dictate the kind of mass transfer process responsible for the release of volatiles. Therefore, depending on the pyrolysis condition, bulk diffusion or forced flow would dominate the mass transfer processes for the release of volatiles. The introduction of cations is thought to result in irreversible changes in the lignite structure and not only control the process of formation but also the amount of volatile precursors and in turn alter the effects of pressure. Valence and catalytic activity of cations seem to play important roles in determining pyrolysis products distribution at elevated pressures.

Increasing power plant efficiency by fuel drying

The process of pre-drying of fossil fuels — in this case raw lignite with a water content of 35 to 55 w% — leads to an increase, of the overall efficiency by 2 to 3 %points achieved by a reduction of primary fuel. The overall efficiency can be increased by up to 5%points by integration of a vapor condenser and energy reintegration. The necessary heat for the drying process is taken from the process cycle in the form of low pressure steam. Economic reasons limit the rest water content of the dried coal between 10 and 12 w%. The present paper discusses the use of process simulation programs for the thermodynamic optimization of the performance of complicated energy systems and presents six variants for increasing power plant efficiency by lignite drying.

Effect of Rhodococcus rhodochrous on the pyrolysis kinetics of Mengen lignite

This paper reports on the pyrolytic behaviour of raw and microbiologically treated Mengen lignite. Two coal samples were pyrolysed in a thermobalance apparatus at atmospheric pressure. Experiments were carried out dynamically by increasing the temperature from 298 to 1173 K at a heating rate of 20 K min −1. The data show good behaviour of the microbiologically treated lignite compared with raw lignite. An increase in the activation energy was obtained after microbial removal of sulfur.

95/06278 Converstion of a former raw lignite heating plant for wood chips utilization

The coal fired thermal power plants plays major role in the power production in the world as they are available in abundance. Many of the existing power plants are based on the subcritical technology which can produce power with the efficiency of around 33%. But the newer plants are built on either supercritical or ultra-supercritical technology whose efficiency can be up to 50%. Main objective of the work is to enhance the efficiency of the existing subcritical power plants to compensate for the increasing demand. For achieving the objective, the statistical modeling of the boiler units such as economizer, drum and the superheater are initially carried out. The effectiveness of the developed models is tested using analysis methods like R2 analysis and ANOVA (Analysis of Variance). The dependability of the process variable (temperature) on different manipulated variables is analyzed in the paper. Validations of the model are provided with their error analysis. Response surface methodology (RSM) supported by DOE (design of experiments) are implemented to optimize the operating parameters. Individual models along with the integrated model are used to study and design the predictive control of the coal-fired thermal power plant.

Relationship between the Activated Carbon Surface Area and Adsorption Model Coefficients for Removal of Phenol from Water

Abstract The present study investigated the relationship between the activated carbon surface area, as measured by the BET nitrogen adsorption method, and its adsorptive capacity. Aqueous solutions of phenol at pH 7 were used. The activated carbons were produced in the laboratory from raw and demineralized lignite. Adsorption experiments took place under equilibrium or kinetic conditions and the results were simulated by mathematical modelling. Freundlich and Langmuir models were used to describe equilibrium, while the Peel-Benedek non-equilibrium model was applied for the kinetic study. The results showed that for activated carbons produced from different starting materials, the adsorptive capacities could not be solely explained by their BET surface area. While laboratory-made activated carbons with a surface area of 300 m2/g demonstrated similar capacities under equilibrium, their kinetic behaviour was different. Activated carbon produced from raw lignite showed faster kinetics, due to wider porosity, which was facilitated by the mineral matter during activation. These results were in agreement with the mass transfer coefficients in macropores and micropores estimated by the Peel-Benedek model. Comparison of a laboratory-made activated carbon, with a surface area of 500m2/g, with a commercial activated carbon having twice the surface area showed that the maximum adsorptive capacity under equilibrium of the commercial carbon was only 35% higher than that of the lab-made carbon. Yet, the mass transfer coefficients of the commercial carbon were one to two orders of magnitude higher than those of the laboratory-produced carbon. Finally, the use of the qualitative D-R plots has been suggested to elucidate the porous structure of the activated carbons.

The influence of fly ash on atrazine and alachlor persistence in corn cultivation soil

The influence of fly ash (raw material lignite from thermal station, pH = 11.2) in the fate of atrazine and alachlor was studied in an experimental corn cultivation soil, under environmental conditions of Ioannina region (N.W. Greece). An amount of fly ash equal to 0.15% p.w. of soil for a depth 0–10 cm was used in a sandy‐clay‐loam soil on the 18th of May 1988 when the sowing of the corn and the application of two herbicides took place. Analyses of soil samples for 240 days, in a period between May 18, 1988 and January 14, 1989 showed that the addition of fly ash decreases the half life of atrazine, from 54 to 47 days and of alachlor from 25 to 22 days. The final results of fly ash addition showed a decrement of atrazine residues of about 42.6% in soil without corn cultivation and 46.6% in soil with corn after 240 days. For the alachlor residues the corresponding decrements were 40.6% in the reference soil and 52.8% in corn cultivation soil, after 118 days.

The effect of demineralization on lignite activation

Activated carbons were produced from raw and demineralized Greek lignites under various experimental conditions using CO 2 as the oxidizing agent. Removal of inorganic impurities was accomplished by acid washing of raw lignite with HF and HCl acid solutions. For the characterization of the activated carbons produced, adsorption of N 2 at 77 K and CO 2 at 298 K was used. Resulting isotherms were analysed by the BET and Dubinin-Radushkevich methods to give an assessment of microporosity. Demineralization brought about a lowering in the reactivity of the acid-washed coal and an increase in the apparent activation energy for reaction. Removal of inorganic matter resulted in activated carbons with very large surface area values and a highly developed microporosity. Surface area values of activated carbons produced from demineralized lignite were up to five times greater than those of activated carbons from untreated lignite, especially at high burn-off. Activation temperature increased the reaction rate, but it did not affect the pore structure of the final products.

The influence of inorganic matter on the pyrolysis of Canadian lignite in a fluidized bed

In low rank coals much of the inorganic matter is present as cations associated with organic carboxyl groups in the coal rather than as discrete mineral phases. By treating the coal with acid the inorganic content is reduced by cation exchange, as well as by acid leaching of discrete minerals. Whole and acid treated samples of pulverized lignite were pyrolyzed in pilot scale (1 to 3 kg coal/h) and bench scale (60 to 100 g coal/h) fluidized bed reactors at atmospheric pressure, 0.45 second vapour-residence time, and temperatures ranging from 500 to 730°C. Yields of char, tar, water and light gases were determined. Removal of inorganic matter from a Saskatchewan lignite resulted in increased yields of tar and total volatile matter, with little effect on the yields of light gases. Increased yields of tar are largely a result of an increased asphaltene fraction in general and specifically of an increased catechol content. Char from acid-washed coal is less reactive to carbon dioxide than is char obtained from raw lignite.

Hydrothermal preparation of low-rank coal-water fuel slurries

Lignite and sub-bituminous coals are by nature high in inherent moisture and oxygen content and low in calorific heating value. As-mined low-rank coals when mixed with water generally produce slurries with low solids content and with heating values generally less than 11.6 MJ/kg. These same slurries are usually unstable and form hard-pack sediments quickly, unless chemical additives or constant agitation are added. The low heating value and poor storage and flow characteristics of these coal-water mixtures discourage the use of raw lignite and subbituminous coals for preparation of slurries for fuel purposes. Hydrothermal conditioning, in a water slurry at temperatures above 230 °C and pressures above 552 MPa, is one method that can significantly aid in the preparation of low-rank coal-water fuels. High-pressure hot-water thermal conditioning of lignites and sub-bituminous coals has been found not only to change both the chemical and physical characteristics of the coal but also to alter the coal slurry's rheological properties. These changes are controlled by process variables (i.e. temperature, residence time, particle size, and mode of processing) and result because of decarboxylation, mild pyrolysis, extraction, dehydration, and surface modification; all of which occur during hydrothermal treatment. Using the hydrothermal process, concentrated low-rank coal-water slurries with heating values approaching or exceeding the heating value of the as-mined coal have been achieved with pseudoplastic flow behavior and stability towards settling, without the use of additives. Pilot-scale studies using a 90-kg/hr process development unit (PDU) are currently under way to produce hydrothermally treated low-rank coal fuel slurries for combustion tests in a pilot-scale, slurry-fed test furnace.

Pyrolysis of a lignite in an entrained flow reactor: 1. Effect of cations on total weight loss

The role of exchangeable metal cations (Ca, Mg, Na, K, Sr and Ba) in the rapid pyrolysis of a Montana lignite has been studied. The effects of variation of the cations present, and cation concentration, on weight loss and pyrolysis kinetics are presented. The reactor utilized was a dilute-phase entrained flow reactor. The reactor conditions decrease the degree of secondary reactions occurring to the primary volatile species and allow a clearer view of the fundamental pyrolysis processes. A model of the heat and momentum transfer in the reactor has been employed to estimate the particle time-temperature history. The results of pyrolysing the lignite samples display a significant role of metal cations. At 1173 K, the presence of metal cations resulted in a decrease in total weight loss at maximum residence time (0.25 s) from 50% (dry inorganic constituent free basis, dicf) for 0 wt% metal cations (acid washed) to 30% (dicf) (raw lignite, 2.8 wt% cations). Data are also presented concerning the maximum weight loss when only calcium, sodium or magnesium exchangeable cations were present. The apparent activation energy obtained from a first-order Arrhenius kinetic treatment is shown to be dependent on the presence of cations.

Pyrolysis of a lignite in an entrained flow reactor: 3. Pyrolysis in reactive atmospheres of air, carbon dioxide and wet nitrogen

The role of the exchangeable cations on pyrolysis in the potentially reactive atmospheres of air, carbon dioxide and wet nitrogen has been studied in an entrained flow reactor. The amount and type of exchangeable cation present has been found to influence the behaviour of coal. In air, it was found that the presence of metal cations results in a decrease in initial weight loss in the reactor. At 0.05 s, weight loss in air at 1173 K was 30% when the metal cations were present and 80% when the cations were removed. While there was a dramatic effect of metal cations on initial weight loss, very little effect on weight loss at maximum residence time (0.25 s) was observed. Pyrolysis of the lignite samples in wet nitrogen and carbon dioxide led to a number of interesting results. Weight loss at maximum residence time for the acid washed lignite (metal cations removed) was virtually the same in nitrogen, carbon dioxide and wet nitrogen. Secondly, the raw lignite lost less weight than the acid washed lignite in all atmospheres, but the presence of carbon dioxide and wet nitrogen resulted in an increase in weight loss over nitrogen. Results are discussed in terms of the effect of metal cations on coal pyrolysis, char gasification and the interaction between the two.

Catalysis of lignite char gasification by exchangeable calcium and magnesium

A Montana lignite was pretreated in either HCI—HF or ammonium acetate. The former treatment replaced cations associated with carboxyl groups by hydrogen, as well as removing essentially all mineral matter. The latter treatment replaced cations by ammonium ions but left the mineral matter intact. The pretreated lignites were then loaded with varying amounts of Ca and Mg, separately or jointly, by ion exchange. Reactivities of chars produced from these exchanged lignites, as well as the raw and pretreated lignites, were determined in air, CO2 and steam. Gasification of exchanged lignites was strongly catalysed by Ca; its activity was not affected by the presence of Mg on the char. At a comparable Ca loading, gasification rates of the 1273 K raw lignite char in the various atmospheres was higher than that of the acid treated 1273 K char but lower than that of the ammonium acetate treated 1273 K char. The former finding is attributed to chlorine retention in the lignite and char; the latter, to enhanced sulphur release during lignite pyrolysis.

Formation and occurrence of cancer-producing hydrocarbons in cereals and possibilities for their reduction

According to the authors' investigations every inhabitant of the GDR takes between 0.2 and 1.0 mg BaP. per year by food consumption including amounts of 0.03 to 0.17 mg on account of cereals and mill products. For the contamination of cereals the following sources are in consideration: environmental contamination on account of industry dust (distant from industry 0.1 to 0.6, near to industry 0.3 to 4.2 micrograms BaP/kg), passing over from soil to plant (with model experiments with soils more than 10 000 micrograms BaP/kg up to 22.3 micrograms BaP/kg dry matter) as well as technologically caused contamination for instance by direct fume-and-gas drying (with the use of raw lignite up to 10 micrograms BaP/kg). As it can be concluded from model experiments BaP passes to flour at milling in dependence of the extraction rate. By separating the husks prior to milling more than 50% of BaP can be removed from the stock.

Enhancement of lignite char reactivity to steam by cation addition

Chars produced from lignites typically have much higher reactivities to gasification than those produced from bituminous coals. This has been attributed previously to the presence of carboxylate salts of inorganic constituents on the lignites. Upon charring of the lignites, the carboxylate salts decompose leaving behind well dispersed inorganic constituents which act as catalysts for gasification. In this study, a raw lignite has been treated with HCl and HF to demineralize it and to increase its carboxyl content prior to exchanging selected cations with the hydrogen on the carboxyl groups. Up to 2.14 mmol of calcium per g of coal could be added using this procedure. Addition of varying amounts of calcium to the lignite resulted in the production of chars containing calcium contents ranging from 1.1 to 12.9 wt %. Such addition resulted in a rectilinear increase in reactivity of the char to steam with increasing amount of calcium added. Maximum reactivity attained was over ten times the reactivity found for the char produced from the raw lignite. At comparable molar loadings of metal cations onto the acid-treated lignite, the chars subsequently produced had reactivities in steam in the order: K > Na ≈ Ca > Fe > Mg. Char reactivity could also be enhanced by the addition of cations to nitric acid-treated char which had been produced, in turn, from demineralized lignite.

Lignite Char: Its Production and Possibilities

Abstract Lignite char is lignite which has been dried and distilled in an oven especially designed for the purpose. About two and one-half tons of raw lignite reduce to one ton of char, the heating value of which is about 12,000 B.t.u. per lb. While raw lignite can be used satisfactorily in large steam-raising operations, the author believes that the search for a means to improve the fuel must continue. American lignites do not briquet well without the addition of a binder, and the Bureau of Mines has therefore been led to investigate the possibilities of an inexpensive carbonizing process and the use of the resulting lignite char direct without briquetting. This process is briefly described in the paper.