CFD Analysis on Biogas Bubble Creation Within a Stirred Tank of a Wastewater Treatment Plant

A mixing strategy for assuring a homogeneous fluid flow inside wastewater treatment plants (WWTPs) is a necessity, in order to keep continuous contacts of substrates and degraders. On the other hand, mixing is an energy-demanding process. Therefore, the power consumption for mixing the fluid flow within bioreactors affects the overall efficiency of WWTPs. The current study aims at evaluating the incorporation of biogas bubble creation on the mixing of WWTP tanks. Computational fluid dynamics (CFD) enables simulating hydrodynamics of multiphase fluid flows injected with bubble parcels. The case is a cylindrical stirred tank, in which the fluid flow is agitated via a rotating mixer. Mixer rotates at various speeds; and for each case, the ultimate fluid flow is captured both with and without bubble creation. Non-Newtonian characteristics of the fluid flow within the tank are considered and k–ε turbulence closure is selected for the model. By a two-way coupling of an Eulerian-Lagrangian platform, velocity fields and the amount of dead volume are analyzed and discussed. Our key finding is that the biogas bubble creation contributes to the reduction of dead volume inside the WWTP tank, when there is no external rotating mixing, or once the amount of mixer rotation speed is low.

CFD Modeling of a Stirred Anaerobic Digestion Tank for Evaluating Energy Consumption Through Mixing

The anaerobic digestion process is an effective means to eliminate the detrimental impacts of cattle manure discharge into the environment, i.e., biochemical contamination and substantial methane emissions, the latter leading to global warming. For proper operation of anaerobic digesters, an efficient mixing provides a relatively homogenous mixture of the feedstock within the tank. This study aims to investigate the mixing process and the total energy consumption needed for stirring by using an asymmetrical mixer. A further objective is to analyze the formation of stagnant volume and the velocity gradient in the digester in order to assure the mixing efficiency of the mixer type. The computational model is implemented as the finite volume method, and the rheological properties of the feedstock are considered. The results are validated by comparing the on-site power consumption of the mixer with the values obtained by the numerical torque. At various mixer speeds, the dead volume does not exceed 0.5% of the digester tank; however, with the increase of the mixer rotation speed, the energy consumption of the mixer increases drastically.

Gas dispersion in the oxygen delignification process

There has been very little knowledge about the state of gas dispersion in the oxygen delignification process, even though this has a major impact on the performance of the reactor. This paper presents a new continu-ous inline method for measuring oxygen bubble size distribution in the reactor, as well as results from studies con-ducted in softwood and hardwood lines. This new measurement worked well, and new information about oxygen bubble size, as well as how different reactor conditions affected the distribution, was obtained. For example: • In the softwood line, the mean volume-weighted bubble size was about 0.1 mm, whereas in the hardwood line, this size was almost 10 times higher. For both lines, there was considerable variation in the measured bubble size over the long term. • For both lines, an increase in mixer rotation speed caused a discernible decrease in the bubble size, and an increase in oxygen charge caused a discernible increase in the bubble size. • In the softwood line, no coalescence of the bubbles in the reactor was observed, but in the hardwood line, some coalescence of the larger bubbles occurred. • In the test conducted in the hardwood line, the use of brownstock washer defoamer caused a discernible increase in oxygen bubble size. • In the hardwood line, reactor pressure had a noticeable effect on the amount of delignification, which indicated that improving mass transfer of oxygen (e.g., by decreasing the oxygen bubble size, in this case) should also have an increasing effect on the delignification.

DEVELOPMENT OF KNIFE EYES ON THE MAKING PROCESS OF ORGANIC BURNING PROCESS OF 7 LITERS FOR UMKM

The planning and design of the blades mixer for the organic slurry dough mixer is the application of the sciences obtained in real college. The main purpose of making blades mixer for this slurry dough mixer is to get an effective, efficient blades mixer design and higher quality organic slurry. With the making of this blades mixer, it is expected to contribute positively in the middle industry engaged in the food industry. The author designed several forms of modeling of blades mixer capable of stirring the organic pulp mixture with a capacity of 7 liters. The blades mixer are planned to use 304 steinless steel Austenitic material. For a planned blades mixer rotation of 35 rpm, and to achieve such a large rotation, pulleys and gearboxes (reducers) take an important role to achieve the planned rotation. The treatment carried out for this organic slurry dough mixer can be in the form of planned and unplanned treatments. With this report, it is expected to be able to add knowledge in the field of engineering.

THE INFLUENCE OF MIXER ROTATION FREQUENCY AND ITS BLADES LENGTH ON THE QUALITY OF THE MIXTURE

The aim of the study is the quality improvement of the feed mixture prepared and substantiation of the design and technological parameters of blade mixer batch- operated. The task is to set the functional dependence between the prepared mixtures quality and the empirical ratio of the intensity of mixing, taking into account the blades length in regard to values of the rotation frequency and the length of the blade of the batch-operated mixer, as well as the definition of rational length of the mixer blades. Improving the quality of mixture requires both the adding of all nec-essary nutrients and feed components into the volume of prepared portion of the mixture as stipulated by the recipe for mixture, and smooth distribution of components throughout the volume of ready feed. Smooth distribution of the mixture components is related to the design and operation of the mixer. Blade mixer batch- operated is one of the effective types of existing mixers, mixing the ingredients of feed with good quality. The article presents the result oriented design scheme of the blade mixer. Positive functions of the mixture quality and the empirical coefficient of mixing intensity included in their composition are assessed taking into account the length of the blades, depending on the rotation speed and frequency of the mixer. The graphic results of experimental studies taking into account the influence of the blade length and the speed of the mixer on the quality of the prepared mixture are given. The increase of blade length and rotation speed improves the quality of the mixture. Recommended blade length is 75...80 mm. With frequency of rotation increase and the length of the blades the total value of the empirical coeffi-cient of the intensity of mixing, depending on the effect of the length of the blades decreases at a slower pace. This is typical of the obtained hyperbolic dependence.

Textural and sensory properties of spreads with sucrose and maltitol

Spreads are confectionery products based on sugar, vegetable fat, cocoa powder, milk powder and other ingredients. Basic properties of these products are good spreadability in wide temperature range (from ambience to fridge temperature), rich creamy chocolate taste, and homogenous smooth structure without oil phase migration. Undesirable attribute of these products is their relatively high energy value (2300 kJ/100 g). In recent years, cocoa cream products with reduced energy values have become very popular among consumers and today they are present in the assortment of many confectionery manufacturers. One way to produce spreads with reduced energy value is the replacement of sugar (sucrose) with adequate sweetener. Maltitol is a low-energy poliol capable to qualitatively and quantitatively replace sucrose. Cocoa spreads with maltitol and with the combination of maltitol and sucrose (produced at different temperatures and mixer rotation speeds) have similar texture and rheological properties compared to the spreads with sucrose. The spreads with maltitol have about 15% lower energy value in comparison to the same product with sucrose.