Oxygenation Efficiency Of Bjt Loop Reactor
OXYGENATION EFFICIENCY OF BJT LOOP REACTOR
B.J. Trznadel
Military Institute of Chemistry and Radiometry, Warsaw, Poland
This paper is an attempt to replace a classical primary waste aeration chamber with a loop reactor of type BJT-250 (bubble jet tank) in order to eliminate, on aphysic-chemical pathway, impurities from petrochemical wastewaters in the sewage treatment plant in ORLEN Refinery in Plock (Poland).
The petrochemical wastewater contains high quantity of various impurities (COD over 5000mg/l), mainly aromatic and aliphatic hydrocarbons, fats, phenols, suspended matter, odorous compounds such as hydrogen sulphide, mercaptans and many others.
Fig.1. Construction scheme of the BJT-40 loop reactor.
For verification of conceived design and construction solution a loop reactor of type BJT-40 was built. The reactor was due to aeration the petrochemical wastewater of flow rate up to 40m3/h. The overall dimensions of the reactor are as follows: diameter - 0.82m, height - 4.5m, diameter of the draft tube - 0.45m, its height - 2m, depth of the air supply nozzle - about 3.2m (Fig.1).
A complete verification investigation was carried out on the described reactor operating in the process of petrochemical wastewater purification. Performed tests indicated the following advantages of the constructed device: relatively small overall dimensions, close type construction which practically eliminating a possibility of emission of pollutants from wastewater to the atmosphere, high degree of reliability thanks to elimination of moving mechanical parts, simplicity of operation and maintenance, very high tolerance to changes in hydraulic load and high mass transfer coefficient (kLa in the range 15-60h-1).
Analysis of experimental data gives possible to compare operational efficiency of BJT-40 loop reactor with others systems of wastewater aeration. Obtained results are presented in Fig.2.
Fig.2. The oxygenation efficiency in the BJT-40 loop reactor: a - fine-bubble aeration, b - medium bubble aeration, c - large bubble aeration, d - SIMPLEX rotor, e - BSK turbine.
The operational conditions may be expressed by following correlations:
- for COD reduction
where w is the ratio of volumetric air flow rate to wastewater flow rate,
-for pressure drop
where Dp is measured in mmHg,
-for loosed power
Analysis of above function leads to conclusion that volumetric ratio of flow rates ought to be about 8, and this value gives the highest COD reduction related to the quantity of loosed power. Optimisation studies of the reactor operational parameters were performed on the basis of obtained experimental data. Moreover in these studies the rules of scale development were taken into account. The new construction of a primary aeration chamber is the final result of optimisation studies. It is proposed to used in pilot scale (petrochemical wastewater flow rate about 250m3h-1) a system consisting of two BJT-250 reactors-in- series with separate stream air supply. A single reactor of such type has following dimensions: diameter - 1.8m, height - 6.5m, diameter of the draft tube - 0.95m, its height - 2.6m, depth of the air supply nozzle - about 3.6m. Such system was installed in the sewage treatment plant in Plock refinery.
It was found that such system is more effective than a standard primary aeration chamber. This system reduces the total suspended matter and COD over 10% than in a case of standard primary chamber. Similarly the reduction of concentration of aromatic hydrocarbons as well as sulphides was higher over15%.
The final effects of the first step of petrochemical wastewater purification (only physic-chemical wastes treatment) using the set of BJT-250 reactors are as follows:
– removal of general suspended matter and hydrocarbons over 90%;
– reduction of COD approximately 50%;
– reduction of sulphides concentration about 30%.
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