Abstract-Black liquor is a by-product of the pulping process in the manufacture of paper. It is a complex mixture of both organic and inorganic chemicals with both chemical value and energy content. To recover these two quantities, the black liquor is concentrated to around 60 -85 % solids concentration and fired into a recovery boiler. In the boiler, the black liquor is sprayed in the form of droplets which fall through the atmosphere of the furnace to the bottom. During this process, the droplet undergoes drying, devolatilization and char burning in succession before coalescing with the smelt at the bottom. The modeling of these processes during the movement of the black liquor droplet is quite complex and in this paper, we attempt to simulate the weight loss during the devolatilization stage by studying the pyrolysis of dry black liquor solids in a muffle furnace. Experiments were carried out at temperatures varying from 973 to 1273 K and for residence times varying from 30 to 180 s. The kinetic scheme of dry black liquor solids decomposition by a single reaction giving gaseous volatiles and char is used. The proposed single reaction model is simulated and the best values of the kinetic parameters i.e. activation energy and Arrhenius constant are found by using the two-dimensional surface fitting non-linear regression algorithm. The results indicate good agreement between predicted and experimental data.
Abstract-In this paper, the drying of black liquor droplets sprayed into the chemical recovery boiler in a pulp and paper mill is examined. The fate of the droplets in the recovery boiler is generally divided into three consecutive stages i.e., drying, devolatilization and char combustion. Drying refers to the removal of water from the black liquor droplets by upward moving hot gases during its flight in the recovery boiler. When the black liquor is atomized in the hot ambience of the recovery boiler, different sizes of droplets are generated, some of which are not desirable with regard to incomplete drying. This creates problems in operation of the recovery boiler. A simple mathematical model is developed to estimate the travel time from the point of injection to the char bed. Simulations were carried out for various parameters including droplet size and suitable droplet sizes determined for safe and economical boiler operation. Index Terms-Black liquor, drying, modeling, recovery boiler, droplet size I. INTRODUCTIONBlack Liquor is generated during the process of pulp production in a chemical digester and this process is called cooking or pulping [1]. Cooking is the process of extraction of cellulose fibers present in the stock by freeing the cellulose from the lignin content. Cooking of the wood chips is carried out at temperatures of around 165 C and pressures of 5-6 kg/cm 2 (g) in the presence of an inorganic chemical solution (consisting of approximately 60 wt% Sodium Hydroxide, 25 wt% Sodium Sulfide and 15 wt% Sodium Carbonate). After cooking, the cellulose fibers are separated by filtration and the resulting filtrate is called weak black liquor. This weak black liquor contains valuable inorganic and organic chemicals. Recovery of these chemicals in the form of either heat energy or chemicals play a crucial role in the overall economics of the pulp and paper industry. The weak black liquor is then concentrated in multiple-effect evaporators and fed into a chemical recovery boiler for recovering heat and chemicals.The droplets are generated by spraying black liquor into the recovery furnace. The droplets, which are essentially spherical in shape, move down in the recovery furnace encountering a stream of rising hot gases. The droplet receives heat from the hot gases, loses water by evaporation and the process continues till all the moisture is removed. This is the drying phase. It may be noted that due to the presence of inorganic solids, the boiling point of the black liquor is elevated to the order of around 20 C above the normal boiling point of water. The dried particles move further down experiencing simultaneous heat transfer and mass transfer (devolatilization). During this process, the temperature of the particle (droplet) increases and the particle finally hits the char bed at the bottom of the furnace.In the char bed, combustion takes place and the hot gases move upwards. The fate of the droplet from the point of injection till it hits the char bed essentially has 3 distinct phases as listed b...
Hydrogeochemical characteristics of Groundwater analyzed in the study area of Coimbatore district by collecting 60 samples from agricultural belt. Groundwater quality for irrigation is determined by several key factors like pH, Electrical conductivity (EC), Total suspended solids (TDS). The cations such as Sodium (Na+), Potassium (K+), Calcium (Ca2+), Magnesium (Mg2+ ) and anions are Hydrocarbon (HCO3), Carbonate (CO3 -), Chlorides (Cl-)and Sulphates (SO4 2-) are tested. The irrigation water quality parameters such as Residual Sodium Carbonate (RSC), Sodium Absorption Ratio (SAR), Chloro Alkali Indices (CA I & CAII), Kelley’s Ratio (KR), Magnesium Hazard (MH), Percent sodium (%Na) and Permeability Index (PI), Soluble sodium Percent (SSP) are computed from the key factors, anions and cations. From the USSL Diagram the samples fall in C2S1, C3S1, C4S1 range. Salinity hazard is too elevated in the study area, all the samples are categorized under high to very high with the values greater than 750 μS/cm. Total dissolved solid in the study area indicated that only 2 locations are unfit for irrigation. SAR and % Na shows that there is no hazard related to irrigation watering. Magnesium hazard in the groundwater is high and indicates 51 sample out of 60 is unsuitable for irrigation. From the study it indicates the groundwater is contaminated with salt content and in most of the area it can be used for irrigation. Keywords: Groundwater, Irrigation water quality, Salinity hazard, Kelley’s ratio, Magnesium hazard
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