Lime Recovery Research Articles

Рекуперация и очистка газовых выбросов целлюлозного производства

For pulp production, large-scale enterprises have been built which, while in operation, are subject to new requirements, different from the design ones, for economic efficiency, labour safety, as well as impact on the local population and the environment. Significant success in this work has been achieved by changing the liquor recovery technology, switching to burning black liquor of increased concentration, which makes it possible to almost completely eliminate the largest source of hydrogen sulfide and methyl mercaptan emissions with flue gases, reduce sulfur losses and improve energy efficiency of soda recovery boilers. Another significant source of soda recovery boiler emissions is a smelt dissolving tank vent. An important technological operation of dissolving molten sodium salts with weak white liquor supplied from the causticization shop takes place in the tank. The modern development of smelt leaching technology is related to the improvement of equipment compatible with the technology of regeneration of chemical reagents for pulp production. Heat exchangers and gas purifiers of “gas-liquid” systems, easier to adapt to technological requirements compared to other systems, are installed on the dissolving tank vent. The installation of such equipment provides the change in the smelt leaching technology, and affects the technology of causticization and lime recovery. This article covers the research of the relationship between the technical solutions ensuring the safety of personnel in the boiler shop, heat and chemicals recovery, as well as purification of gas emissions and the changes in the technology of smelt leaching in the soda recovery boiler of the pulp mill. On the basis of experimental data and a mathematical model of the movement of the vapour-gas mixture in the smelt dissolving tank vent, the technological feasibility of installing heat exchangers at different heights of the vent and the possibility of effective purification of gas emissions using a direct-flow sprayer have been considered. The applicability of the irrigation of the steam-gas flow with weak white liquor, which is formed during the cycle of chemical regeneration in pulp production, as well as the conditions for ensuring reliable operation of gas purification equipment, have been investigated. The quantitative characteristics of the necessary change in consumption and composition of weak white liquor and the methods of its supply to the dissolving tank have been obtained.

Eggshells from agro-industrial waste for the recovery of lime, portlandite, and calcite nanoparticles through the lime cycle: A circular economic approach

This work focused on the study the lime cycle for samples obtained from agro-waste of chicken eggshells, mainly composed of calcite (CaCO3), in the context of circular economy concept and for nanotechnological applications. The thermal analysis (TGA/DSC) analyzed the transformation temperatures of the individual phases. Based on these results, the eggshells were calcined at 850 °C to ensure the complete conversion of calcite into lime (CaO). The lime was then hydrated with distilled water to convert it into portlandite (Ca(OH)2). The samples belonging to this cycle were structurally characterized using X-ray diffraction, and the vibrational states were identified using Fourier transform infrared spectroscopy. Scanning Electron Microscopy was used to study the changes in morphology and crystallite size. This showed that all compounds along the cycle are microparticles consisting of nanocrystals, which correlated with the Dynamic Light Scattering results. The Zeta potential was used to determine the surface charge of the samples and shown a variety of results due to the different transformations during the cycle and the mineral content of the eggshells as shown by the results of the ICP technique.

Amelioration of subsurface acidity in the south-west of Western Australia: downward movement and mass balance of surface-incorporated lime after 2-15 years

Twenty-one lime trial sites in the south-western agricultural region of Western Australia (WA) ranging in duration from 2 to 15 years were sampled in 1995 to a depth of 40 cm in 10-cm increments. In each case, samples were taken from both control plots and those with highest lime rates; additionally, samples were taken from plots with intermediate lime rates at 3 trial locations. Lime had been incorporated at rates of 2–12 t/ha within the top 0–10 cm layer at 20 of the sites, and at 15 t/ha within 0–20 cm at the remaining site. The following measurements were made: all samples, pH (1 : 5 0.01 M CaCl 2 ) and exchangeable cations (1 : 10 0.1 M BaCl 2 ); selected depths, undissolved carbonate; selected samples, total Ca (1 : 10 0.2 M HCl) and exchangeable Ca (1 : 10 0.1 M BaCl 2 buffered to pH 8.2). The pH of the unlimed subsurface was between 4.0 and 4.5 at 10–20 cm for 15 sites, at 20–30 cm for 7 sites, and at 30–40 cm for 2 sites. In addition, 3 of the unlimed sites had a pH =4.0 at all of these depths. Where lime had been applied, the pH was significantly (P < 0.05) higher than in the controls by at least 0.2 units for 13 sites at depths of 10 cm below the depth of lime incorporation. The same significantly elevated pH was found for 5 sites at depths of 20 cm and for 4 sites at depths of 30 cm. At 5 sites that had also been sampled 3 years previously, the subsurface pH had increased within 4–7 years of liming with 2.5–5 t/ha. Where added lime could be accounted for, the amount of lime added explained 65% of the variation in the residual lime effect at a depth of 10–40 cm. Over all of the wheatbelt trials this represented an average downward movement of lime to a maximum depth of 40 cm of at least 8.3 kg/ha.year.t CaCO 3 applied (range 0–22.5). Increased exchangeable Ca corresponded with a decrease in other base cations in only 2 trials. Decreases in exchangeable Al corresponded with increases in both pH and exchangeable Ca, but were less than the Ca increases. Precipitation of exchangeable Al represented an average of about one-sixth of the pH buffering capacity. Mass balance for Ca was achieved in 11 out of 20 cases in the wheatbelt, if Ca loss as nitrate was assumed to occur at rates of leaching published for WA. Lime recovery on the basis of pH increase was lower. The quantity of lime accounted for by Ca in the added and the residual undissolved lime, plus the increase in exchangeable Ca, ranged from <10% to >90%, with <50% in 9 of 19 cases at 15 trials. Non-exchangeable Ca in HCl extracts of a subset of surface samples was from 1% to 60% of Ca not accounted for. In 6 cases the Ca deficit exceeded plausible rates of acidification, and at 2 of these marked decreases of about 1 t/ha undissolved CaCO3 corresponded with episodes of high wind speed and observations of soil erosion. The implications of possible losses of lime by erosion are discussed.

Lime pretreatment of crop residues bagasse and wheat straw

Lime (calcium hydroxide) was used as a pretreatment agent to enhance the enzymatic digestibility of two common crop residues: bagasse and wheat straw. A systematic study of pretreatment conditions suggested that for short pretreatment times (1–3 h), high temperatures (85-135°C) were required to achieve high sugar yields, whereas for long pretreatment times (e.g., 24 h), low temperatures (50–65°C) were effective. The recommended lime loading is 0.1 g Ca(OH)2/g dry biomass. Water loading had little effect on the digestibility. Under the recommended conditions, the 3-d reducing sugar yield of the pretreated bagasse increased from 153 to 659 mg Eq glucose/g dry biomass, and that of the pretreated wheat straw increased from 65 to 650 mg Eq glucose/g dry biomass. A material balance study on bagasse showed that the biomass yield after lime pretreatment is 93.6%. No glucan or xylan was removed from bagasse by the pretreatment, whereas 14% of lignin became solubilized. A lime recovery study showed that 86% of added calcium was removed from the pretreated bagasse by ten washings and could be recovered by carbonating the wash water with CO2 at pH 9.5.

96/05995 Recovery of lime, sulfur, and iron from gypsum and pyrite wastes

96/05995 Recovery of lime, sulfur, and iron from gypsum and pyrite wastes

Recovery of Lime, Sulfur, and Iron from Gypsum and Pyrite Wastes

Currently, gypsum and pyrite, two major wastes generated by the coal combustion industry, have to be land-filled. The feasibility of a new approach of recovery of lime, iron, and sulfur products from these wastes is discussed in the present work. By thermal decomposition of pyrite, 42% of the sulfur is recovered and pyrrhotite is produced. A thermodynamic analysis shows that the recovery of iron and lime from pyrrhotite and gypsum in a single-stage process is not feasible. Instead, the process has to consist of two subsequent stages. The first is the reduction of pyrrhotite with carbon in the presence of lime to produce iron, calcium sulfide, and carbon monoxide, followed by reaction of calcium sulfide with gypsum to produce lime and a concentrated sulfur dioxide stream. The kinetics of the reactions involved in the two-stage process is studied using thermogravimetric analysis. The reaction rates are favorable above 950 °C and depend on initial reagent concentrations. The effectiveness of magnetic separat...

Dewatering Chemical-Primary Sludges

The efficiency and the cost of dewatering lime and alum generated physical-chemical treatment sludge were developed utilizing a continuous vacuum filter and a solid bowl conveyor centrifuge. Centrifugal dewatering included evaluation of both single-stage and two-stage classification dewatering. The evaluation of the data showed that lime recovery was economical with both a single and two-state centrifugal as well as vacuum filter above the plant size of 25,000,000 gal/day. Tables show the comparative cost of dewatering the lime and alum sludges for various sizes of treatment plants and with costs itemized for capital and operating considerations. Vacuum filters are the least-cost approach based on the results of the field studies. The paper also shows the process effects of varying operating parameters for these centrifuge and vacuum filter operations.

Lime Recovery and Reuse in Primary Treatment

Dosing lime to municipal wastewater prior to primary sedimentation tanks and the subsequent recovery, classification and recalcining of the primary sludge which is rich in calcium carbonate, was studied in detail by monitoring a 1,500,000 gpd test facility in Contra Costa County, California. A definite improvement in primary treatment performance occurs when the recalcined lime is introduced to the sewage flow, compared to the performance achieved when only virgin lime is used in the process. Primary phosphorus removals averaged 96% when steady-state recycle was established, with average BOD removals of 73% and suspended solids removals of 92%. Continued recycle of the lime causes a buildup in inert fractions such as silica, which are partially removed by a dry classification of the recalcined material. Close agreement was obtained between the observed solids constituent levels and the levels calculated by a specially designed mathematical model of the lime recycling process.

Lime Recovery Process Mathematical Model and Synthesis of Automatic Control System

Lime required for the liquor causticizing process is obtained by way of recovering the lime sludge in rotary furnaces. By analysing the physical and chemical processes that come about in a lime recovery furnace a mathematical model of the object was developed comprising a system of non-linear differential equations in partial derivatives of the 1st order. To ensure steady-state operational conditions for the furnace a boundary-value problem algorithm for the system of conventional non-linear differential equations had been worked out to be solved by the application of a digital computer. Static characteristics of the object were studied and the linearization of the equations was carried out. The linear differential equations of the partial derivatives were reduced to a system of conventional differential equation combining the variables at the integration interval boundaries. This has been achieved by the approximated length integration and with the help of the Ermit interpolation polynomicals. The dynamics of the object is investigated by the series development of the transition functions with reference to the moments of the impulse transfer function. Therewith an algorithm was suggested for obtaining the impulse transfer function moments directly from the system of differential equations without the application of complicated transfer function. The synthesis of the open and closed part of the combined automatic control system is accomplished with regard to the impulse transfer function moments of the multiple-bound object.

New Approaches to Wastewater Treatment

A report on some aspects of the research and development work being carried out on waste treatment technology by the Cincinnati Water Research Laboratory of the Federal Water Polution Control Administration (FWPCA) is presented. Pilot plant activities as well as large-scale treatment plants supported partially by FWPCA Research and Development Grants to cities, sanitary districts and states are included. The individual projects range from single-unit processes to complete treatment systems incorporating biological, chemical and physical treatment techniques. Project flows range from 200 gpd to several million gpd. Project objectives include: (1) Technical and economic evaluation of a process or a complete treatment system, or (2) Development of methods for reducing water pollution of a given type or at a specific location. An example of the latter would be the production of water suitable for underground recharge to prevent salt water intrusion, or for reuse in industrial, agricultural, recreational or other applications. Typical treatment techniques are two-stage lime precipitation with lime recovery and reuse, granular activated carbon adsorption, and a variety of biological and chemical techniques for removing the algal nutrients, nitrogen and phosphorus.

Techniques and Economics of Calcining Softening Sludges: Joint Discussion

This joint discussion on the techniques and economics of calcining softening sludges consists of two papers: Calcination Techniques, by William B. Crow; and, Miami Lime Recovery Plant, by Claude F. Wertz. The first paper discusses recalcination of softening plant sludge including the economics of calcination, existing installations, rotary‐kiln process, pellet‐seeding calciner, and the Gainesville Plant. The second paper discusses a Miami lime recovery plant, including the construction of the plant, thickening of sludge, dewatering of sludge, rotary kiln, stack gas scrubber, carbon dioxide reuse, central controls, lime transport and storage, and operating statistics.

Lime Recovery From Water Softening Sludges

Journal AWWAVolume 33, Issue 4 p. 741-748 Article Lime Recovery From Water Softening Sludges Howard J. Sowden, Howard J. SowdenSearch for more papers by this author Howard J. Sowden, Howard J. SowdenSearch for more papers by this author First published: 01 April 1941 https://doi.org/10.1002/j.1551-8833.1941.tb17233.xCitations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume33, Issue4April 1941Pages 741-748 RelatedInformation

Lime Recovery from Spent Causticizing Mud.

Lime Recovery from Spent Causticizing Mud.