Mathematical Modeling & Engineering Design of Wastewater Treatment Unit for Al-Kut Gas Filling Company

New talented treatment method without chemicals and with minimum operational cost was performed to treat industrial waste water discharged by a hydrostatic test performed on the gas bottles maintenance workshops to reuse it. A common method by Tarleton and Wakeman was used to select the general treatment philosophy, The implementation of this study was carried out on three stages, water sample analysis, simulates the proposed preliminary design and detailed engineering designing for the first stage, a sample of waste water was brought from Al-Kut Gas Filling Company maintenance section and tested for settling, aeration, and filtration. The experiments showed that the most of sediments were insoluble but rather than suspended in water and can be removed by settling. Furthermore, aeration test showed that concentrated Thiophene odor in water was removed at 50 C of water with diffused air bubbling. On the other hand, filtration of using 10 Micron filter paper was achieved to eliminate the rest of tiny sedimentation. Secondly, general dimension of equipment was calculated by engineering design equation according to qualitative and quantitative analyses of waste water. Accordingly, a set of experiments of simulation using ANSYS V19.0 and Eulerian – Eulerian as mathematical model were performed for the 3D two phase flow sedimentation tank with capacity of 5 m3/hr to find the optimum sedimentation performance by testing of the modifications on the tank geometry (baffle depth, distance between baffle and inlet, hooper). Simulation results showed that the optimum tank geometry (0.86 m Baffle depth with inclined part, 2.5m distance between baffle and inlet, hooper within V type geometry W=1.67m/0.29 m, D=1.03 m and tank dimension (L=10m, W=2.5, H=2.5 with slope angle = 2o) with 49.5 volume % in sediment layer with a minimum sediment layer height. This work is licensed under a Creative Commons Attribution 4.0 International License. Journal of Petroleum Research and Studies PISSN: 2220-5381 EISSN: 2710-1096 Open Access No. 34 part 1, March 2022, pp.296-316 297 The third stage included an accomplishment of the Preliminary and detailed engineering design of the entire unit by SOLIDWORKS software to be ready for prototyping.


Introduction
Al-Kut Gas Filling Company has maintenance and inspection section for defected LPG cylinders. The damaged cylinders enter the maintenance workshop as part of cutting, welding and additions such as clamps and bases and sometimes longitudinal welding of the cylinder if needed according to the type of defect found in cylinder as an initial stage of maintenance. In the second stage, the hydrostatic check is carried out using water and air. The inspection system consists of three lines, with a capacity of 150 cylinders/line with average 6 hours of work per day. Water obtained from one cylinder is 26.2 liters at a pressure of 35 bar, the water is recovered from the cylinder back to the tank that feeds the testing system to be used again in the followed cylinders. The capacity of the feeding tank is approximately 4 cubic meters for each line where the pollutants are accumulated for a period of 22 working days of continuous inspection.
After that period, the wastewater is replaced with fresh water from (Raw Water) which is the main source of the plant. In other words, each tank is used to check 3300 cylinders before replacing it with fresh water. Therefore, welding slag, cutting pieces, clay and the remains of the inner lining of the cylinder (iron and metal oxides) are concentrated in this water. Additionally, the strong smell of Thiophene is continuously released to the atmosphere due to open tanks to the environment of maintenance section. As a result, the wastewater is discharge to the channel to pollute the river and therefor, fined is charged by Ministry of Environment representors whenever site is visited. In the last stage, the cylinder is dyed to prepare for filling. This study presents a design proposal for an industrial wastewater treatment Unit for LPG cylinders repair workshop with a production capacity of 5 m 3 /hr and a simulation of the Unit's work and detailed designs.

Material and methods
A proposed prototype for the processing Unit was built based on:

Finding the best technology to recycle the test water of the cylinders
Based on laboratory experiments and analyses of the test water and the sequence of operations required for the treatment, a common method for selecting the optimal techniques for separating pollutants from water was developed by the two scientists, Wyckman and Tallerton [1]. Through a series of procedures and tests, where a mini-list of the optimal techniques for treatment is selected according to the methodology shown in Figure ( (2), (3) and (4) respectively. Thus, the mini-list is selected for the optimal treatment from the expanded list of techniques, which includes the mechanism for evaluating the qualitative performance of appropriate techniques [1][2][3].

Preparing the initial designs for the first stage using Computational Fluid
Dynamic simulation programs.
In order to find the best engineering model to send to the final design stage, Computational Fluid Dynamic (CFD) as a Simulation program which is currently used by international design companies to simulate manufactured models using complex programs such as ANSYS was selected for this process. it is considered the pioneer in simulation programs to detect strengths and weaknesses in designs based on fluid flow equations, and by using complex triple differential and integral equations. Therefore,  The simulation was carried out by using Eulerian-Eulerian model with the Standard K-ξ Model. In order to be considered a correct choice for the mathematical model, it must be compatible with the outputs of practical experiments to reduce the percentage of error. A practical experiment was conducted for the sedimentation process by taking  (6) and (7).   Table 1 and Figures (10 to 17).

Heating Tank ANSYS Results
The

Aeration tank results
Aeration section is the largest part of the tank, and it is open to atmosphere and according to the design, it is either exposed to the air or attached with activated Carbon filters to absorb the Thiophene from the polluted water. The compressed air is distributed inside the tank by means of distribution discs (diffusers), which are spread along the length of the tank and work to transform the flowing air into small bubbles to increase the surface area of contact between air and water as depicted in Figure (22).

Fig. (22): Shows the distribution on diffusers on the aeration tank length
More than a hundred aeration tank simulation experiments have been conducted using mathematical models of fluid flow by using the models (VOF, Mixture and Eulerian Model) and the Implicit models system at each stage. Several constants were changed to reach the best result for the contacting area between water and incoming air and the results reflected to phase volume fraction for each phase on the graphs as shown in Figure (

Unit Design Using SOLIDWORKS
Preparing the final designs using SOLIDWORKS program, in which the exact details and calculations necessary for implementation on the ground are determined. Thus, it is easy to use and take into account the automation process of total capacity that can be increased when necessary depending on the simulation output. The processing unit consists of the following main procedures: -1-Sedimentation unit for clays, minerals, iron slag and its accessories.

3-Filtration unit and its accessories.
4-Control unit and its accessories.  1-Activated Carbon layer, which is used to remove the residual sulfur or thiophene odor, as well as any residual chemical substances especially organic compounds from the water when filtering as first layer in the filter.
2-Anthracite layer is used to remove the turbidity of water and to purify water from small particles.
3-Sand layer is used to purify water from small particles in size.
4-Garnet layer, which has a small granular size with a high density and used to purify the remaining minutes in the water.
5-Gravel layer is used to prevent clogging of the pipes at the bottom of the filter by sand from the upper layers.  Table (2) shows the specification with sheet No.
All design sheets will be attached.

Conclusion
Recycling wastewater of maintenance section in the LPG Gas filling company by designing, simulation and engineering Unit for treatment was suggested. Firstly, selecting path processing technology for treatment based on performing water analysis in the laboratory. Thus, configure out that the Unit is consist of three main parts Precipitators, Aeration, Filtration. Secondly, simulation of the preliminary design Unit using Ansys fluent V.19 (Computational Fluid Dynamic) to mimic the process of sedimentation of particles according to high rate of precipitation that means multimodification geometry of precipitator and heating zone of the first and second part of Unit to reach best configuration. Eventually, the last part is to engineering Unit on the ground by using Solid work program software to determine the practical work as cost and reliable execution steps fitted with area available and issues may raise as obstacles.