Numerical Investigation of the Flow Characteristics of Slurry Manure in a Digestion Tank

Abstract

Animal manure, agricultural wastes and sewage sludge are the most widely used organic wastes in biogas production. In our country, manure from animals such as cattle, sheep and chickens is an important source for biogas production. The mixing process in the digestion tank of the reactors used for biogas production significantly affects the biogas production efficiency. In recent years, it is known that the geometric structure of the digestion tank where the mixing process is carried out also affects this efficiency. In the mixing process, the most commonly used mixing type is mechanical mixing with the help of an propeller/impeller. Due to the high cost and time-consuming aspect of experimental studies, in recent years, the flow characteristics inside the digestion tank have been studied with the help of computational fluid dynamics software. In this context, velocity, turbulent eddy dissipation rate and turbulent kinetic energy distributions in the velocity range 50-175 rpm were investigated in a 60° slope digestion tank with a 6-flat-bladed impeller and the potential effects on biogas production were interpreted. The working fluid in the tank is considered by modeling dairy cattle manure as a non-Newtonian fluid. The results show that the velocity, turbulent kinetic energy and turbulent eddy dissipation rate distributions are generally more effective in the impeller region and at the impeller blade tips. In addition, as the impeller angular velocity increased from 50 rpm to 175 rpm, the amount of volume in the tank with velocity values higher than 0.1 m/s increased from 0.000323 m3 to 0.00262 m3.

Keywords

• Biogas
• digester tank
• mechanical mixing
• renewable energy
• CFD.

Çürütme Tankında Bulamaç Şeklindeki Gübrenin Akış Karakteristiğinin Sayısal Olarak İncelenmesi

Öz

Biyogaz üretiminde en yaygın olarak kullanılan organik atıkların başında hayvan gübreleri, tarımsal atıklar ve atık su çamurları gelmektedir. Ülkemizde sığır, koyun, tavuk gibi hayvanların gübreleri biyogaz üretimi için önemli bir kaynaktır. Biyogaz üretimi için ise kullanılan reaktörlerin çürütme tankında meydana getirilen karıştırma prosesi biyogaz üretim verimini önemli ölçüde etkilemektedir. Son yıllarda, karıştırma prosesinin gerçekleştirildiği çürütme tankının geometrik yapısının da bu verimi etkilediği bilinmektedir. Karıştırma prosesinde en yaygın kullanılan karıştırma tipi bir karıştırıcı/pervane yardımıyla yapılan mekanik karıştırmadır. Deneysel çalışmaların yüksek maliyetli ve zaman alıcı olmasından dolayı son yıllarda çürütme tankı içindeki akış karakteristiği hesaplamalı akışkanlar dinamiği yazılımları yardımıyla incelenmektedir. yararlanılmaktadır. Bu bağlamda, 60° eğimli ve engelleyicili bir çürütme tankında 6-düz-kanatlı karıştırıcı kullanılarak, 50-175 rpm hız aralığındaki hız, türbülans eddy disipasyon oranı ve türbülanslı kinetik enerji dağılımları incelenmiş ve sonuçlar biyogaz üretimi üzerindeki olası etkileri yorumlanmıştır. Tank içindeki çalışma akışkanı süt sığırı gübresinin Newtonyal olmayan akışkan olarak modellenerek ele alınmıştır. Sonuçlar, hız, türbülans kinetik enerji ve türbülans eddy disipasyon oranı dağılımının genel olarak karıştırıcı bölgesinde ve karıştırıcı kanat uçlarında daha etkili olduğunu göstermektedir. Ayrıca, karıştırıcı açısal hızının 50 rpm’den 175 rpm’e yükselmesiyle tank içinde hızın 0,1 m/s’den daha yüksek değerlere sahip olduğu hacim miktarı 0,000323 m3’den 0,00262 m3’e kadar yükselmiştir.

Anahtar Kelimeler

• Biyogaz
• çürütücü tankı
• mekanik karıştırma
• yenilenebilir enerji
• HAD.

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