Tubular Reactor Analysis

Tubular Reactor Analysis
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Tubular Reactor Analysis
EXECUTIVE SUMMARY
Ethanol manufacturing, whereby ethyle acetate and sodium hydroxide act as input to produce sodium acetate and ethanol, is of significant economic interest, and indeed accounts for an active research and development field due to its prominence as a 2nd order kinetic reaction. Among the available and acknowledged conventional processes is the use of tubular reactors that represent one of the most important industrial processes for ethanol production. These systems become necessary after remarkable developments were reported in terms of improved reactor activity. However, for the system to be used in an efficient manner, it must be personalized. In this respect, the present proposal is aimed at highlighting the important aspects of tubular reactors, with the strategies applied and outcomes summarized with respect to Acrid Chemicals Company (ACC) that seeks to improve its operations. Currently, the company is operating a 5.89 liter capacity tubular reactor that works at a set temperature of 25oC to achieve a 64% conversion rate. The company intends for the new reactor design to achieve a confidence at 95% and conversion at 90%. To facilitate the determination of an optimized reactor design that would achieve the set conditions, laboratory experiments were carried out in which calculations revealed that the ideal reactor design should be 18.64 m in length, 0.05 m in diameter, have a capacity of 36.

6 liters and operate at 50oC temperature. Although the proposed reactor design is expected to cost $3,229 to set up, marking it as costing $2,003 more than the base design, the cost difference would easily be recuperated from its larger capacity that allows it to produce 132,600 additional moles of ethanol after operating 8500 hours every year with the additional ethanol producing a revenue of $3,570. As a result, a tubular reactor design that best fits the company has been presented for consideration.
STATEMENT OF THE PROBLEM
Tubular reactors are designed as within a single tank that either contains one long reactor covering the whole tank or many short reactors that run the length of the entire tank. Also known as continuous stirred tank reactors, they are described as plug flow reactors that are intended to ensure that the concentration or reaction rate does not vary along the tank radius even as the concentration changes along the tank’s length. The reactors are intended to handle material primarily in the gas phase to include high temperature, continuous production, heterogeneous, fast, and large-scale reactions (Luyben, 2007; Mann, 2009). The reactors are a preferred choice for the identified reactions because they offer good heat transfer, continuous operations, low labor and operating costs, and high conversion per unit volume. Still, their use is accompanied by disadvantages, to include cleaning them requires shutting down which may be expensive, poor control of temperature, and the existence of undesired thermal gradients (Nauman, 2008; Vrentas, J. & Vrentas, C., 2013).
In the present case, ACC is in need of a new tubular reactor design. The company operates a reactor that saponifies ethyle acetate through an inlet system for 0.1M ethyle acetate and 0.2M sodium hydroxide to produce sodium acetate and ethanol. The flow rate is at 0.6 m3/hr. The reactor parameters are 0.05m for the inner diameter, 3m for the length and 25oC for the temperature with the reaction being isothermal. Based on this parameters, the reactor has a conversion of 64%. The company intends to evaluate design proposals for a new reactor with new operating parameters to include 95% confidence and 90% conversion, as well as the capacity to operate at 30oC, 40oC and 50oC temperatures. At its conclusion, this report will recommend a tubular design that meets the company’s reactor design needs in terms of optimal temperatures and cost analysis.
PROPOSED SOLUTION
The proposed solution entailed determining the design parameters that would meet the set conditions. This is based on the awareness that the temperature, capacity and time parameters can be met by designing a reactor that has the appropriate wall thickness, length, and diameters. The resultant design represents a component of cost estimation. As such, the design competitiveness, economic feasibility, and operating life become principal assessment criteria for the reactor. Based on this awareness, a laboratory experiment was proposed and carried out to determine the feasibility of setting up a tubular design that met the conditions set by the company. Firstly, a watertight glass reactor vessel was set up inside a stainless steel frame that had adjustable feet to facilitate mounting. The coiled tubular section had a length of 20m with a capacity of 0.4l. The vessel was designed to comprise components that include a stainless steel plate with a heating element at the bottom, intake and outlet feed connectors, thermometer, stirrer, and thermocouple, and drainage. Secondly, the vessel was connected to a water supply that functioned as a cooling system, with the water flow controlled by a solenoid valve that took in cold water while the hot water was extruded through a drainage system. Thirdly, the intake was linked to two feed tanks linked to two centripetal pumps and each one carrying a single reactant. Fourthly, the outlet was linked to a sampling pipe and sump tray to facilitate the collection of the products that would then be drained into a hazardous water drum. Fifthly, the reactor was linked to a power supply to manage the heating element and controls. Finally, the system was connected to sensors that controlled temperature, stirring, and pumps’ flow rate (see Appendix I). The experiment was then run with the results noted with the focus being on the reactants and products concentrations and volumes, as well as the experiment’s run time. The design applied in the experiment was determined as appropriate with the functional design modeled around the experiment design. Based on the results, it was determined that the proposed reactor design would be modeled around the laboratory experiment design. The results obtained from the experiment were subjected to analysis, revealing that the optimum operating parameters were 50oC temperature, capacity of 36.6 liters (0.05 m diameter and 18.64 m length) to ensure conversion at 90% and confidence at 95%.
JUSTIFICATION
ACC already operates a plug flow reactor to imply that it is comfortable with this type of reactor. This does not mean that this is the best type of reactor. Rather, it has its advantages and disadvantages but changing to use another reactor would force the company to set up new operating procedures. Using the proposed plug flow reactor would allow the company to enjoy continuous operations with the products produced as a single batch and not in many batches. The result is consistency in product concentration. In addition, the design includes a jacketed reactor that is considered favorable since it minimizes heat losses. Also, the design includes a constant diameter between the reactants’ inlet and products’ outlet, which eliminates flow stagnation especially in areas where deposits are likely to aggregate and form scales. In essence, the diameter has been kept small enough to facilitate fluid velocities that exceed critical values that would allow solids to aggregate (Luyben, 2007). Besides that, the reactor design is accompanied by lower costs and higher conversion percentages.
Additionally, the proposed reactor design can handle materials at high temperatures thereby making it suitable for the current situation since the reactions will occur at temperatures of about 50oC. The high temperature is considered favorable because it is accompanied by a high reaction rate since it increases the collision frequency for the reactants. This means that higher reactor temperature will allow the reacting particles to move faster and collide more often thereby speeding up the reaction rate that produces the alcohol (Mann, 2009). It is important to note that there are other reactor design that the company would have applied, although they are also accompanied by advantages and disadvantages with comparative analysis revealing that plug flow reactor offered the best alternative. One of the alternatives is the continuous stirred tank reactor that similarly allows for continuous operation but is plagued by lower conversion rates. Another option is batch reactors that operate in batches to facilitate lower costs incurrence and downtime for cleaning and maintenance purposes. Overall, a plug flow reactor would be ideal for the present case since ethanol production is best achieved using continuous operations and at higher conversion rates (Nauman, 2008). As such, plug flow reactor presents the best alternative for serving the needs of ACC in ethanol production.
COST ANALYSIS
Cost analysis was conducted to determine the costs that ACC would incur and save, as well as the revenues expected from applying the proposed solution. In this case, the existing reactor design presented a capacity of 5.89 liters with a length of 3 m. The cost of setting up this reactor was $1,226. In contrast, the proposed reactor design to be constructed on ACC premises would have a capacity of 36.6 liters, length of 18.64 m and cost $3,229 to set up. Given that the reactants would remain the same for the existing reactor and proposed reactor design, it was determined that 510,000 moles of ethyl acetate and 1,020,000 moles of sodium hydroxide would be required to produce 326,400 moles of ethanol in the existing reactor design and 459,000 moles of ethanol in the proposed reactor design. The output difference is noted because the current reactor has a 64% conversion rate while the proposed design has a 90% conversion rate. This would increase the production by 40.63% such that at a selling price of $1.75 for every gallon of ethanol produced, the base design would produce ethanol worth $8,789 while the proposed reactor design would produce ethanol worth $12,359. This implies that applying the new design would allow ACC revenues to increase by $3,570 if the input quantities remained the same, thereby allowing the company to recuperate the $2,003 extra costs it incurred from setting up the larger reactor (see Table 1).
Table SEQ Table * ARABIC 1. Operating parameters for the existing and proposed reactor designs
Parameters Existing reactor design Proposed reactor design
Length 3 m 18.64 m
Volume 5.89 liters 36.6 liters
Operating temperature 25oC 50oC
Annual operating time 8,500 hours 8,500 hours
Ethyl acetate input per year 510,000 moles 510,000 moles
Sodium hydroxide input per year 1,020,000 moles 1,020,000 moles
Ethanol output per year 326,400 moles 459,000 moles
Ethanol revenue (at $1.75 per gallon) $8,789 $12,359

CONCLUSION
One must accept that the proposed tubular reactor offers an opportunity for the company to increase its capacity and revenue, while improving operations. This has been ascertained by the chemistry analysis calculations where it has been revealed that operations at 50oC to ensure conversion at 90% and confidence at 95% is best achieved by a tubular reactor design that has a 36.6-liter design to include a diameter of 0.05 m and length of 18.64 m. Additionally, analysis regarding output and costs indicates that the proposed design would increase operational efficiency by 40.63%. Besides that, proposed design has also been shown to be superior to the other reactor designs that include continuous stirred tank reactor and batch reactor. Based on this report, it is proposed that ACC should actively seek to set up a 36.6-liter capacity tubular reactor with 0.05 m by 18.64 m to improve operational efficiency and increase revenue.
References
Luyben, W. (2007). Chemical Reactor Design and Control. Hoboken, NJ: John Wiley and Sons.
Mann, U. (2009). Principles of Chemical Reactor Analysis and Design: New tools for industrial chemical reactors operations (2nd ed.). Hoboken, NJ: John Wiley and Sons.
Nauman, B. (2008). Chemical Reactor Design, Optimization, and Scaleup (2nd ed.). Hoboken, NJ: John Wiley and Sons.
Vrentas, J. & Vrentas, C. (2013). Diffusion and Mass Transfer. Boca Raton, FL: CRC Press.

APPENDICES
Appendix I: Laboratory design for tubular reactor

Figure SEQ Figure * ARABIC 1. Tubular flow reactor

Figure SEQ Figure * ARABIC 2. Top plate details

Figure SEQ Figure * ARABIC 3. Control panel

Figure SEQ Figure * ARABIC 4. Conductivity meter for determining conductivity of stream as it exits reactor into sample cup

Figure SEQ Figure * ARABIC 5. Auto-Titration unit for back titration