Chapter 5: Experimental Apparatus and Procedure Used in This Study
5. Description of the experimental apparatus and procedure
5.2. Experimental apparatus
The schematic diagram of a non-visual isochoric apparatus used in this study is depicted in Figure 5.1. A photograph of the experimental set-up is shown in Figure 5.2. In the following section, the specifications of each item are presented.
L M
D E
A B C
F G H
I
J K
N
Q P
R S T V U
W X
Y
Z Z
To atmosphere
C C AA
G O
R
Figure 5.1. A schematic diagram of the static high pressure apparatus used in this study. AA, mixer shaft; A, high pressure equilibrium cell; B, stirrer; D, pressure transducer; E, data acquisition system; F, temperature probe; H, stirrer motor; HP; hydraulic hand pump; J, drain line; K, thermos-statted bath; M, cold finger; N, syringe for injecting solution; O, gas cylinder; P, vacuum pump; R, mechanical jack; PT, pressure transmitter; R, regulator; S, drain valve; Z, bolts.
59 5.2.1. The high pressure equilibrium cell
The main part of the experimental apparatus is a stainless steel high pressure equilibrium cell with the internal volume of approximately 40 cm3 which can withstand pressures up to 20 MPa. A magnetic stirrer ensures agitation to facilitate good mixing in order to reach equilibrium quickly. Different parts of the high pressure equilibrium cell are illustrated in Figures 5.3 and 5.4. The equilibrium cell can be loaded/ evacuated through a hole placed at the top-left of its body with a diameter of 1/8’. The pressure of the cell was measured using a pressure transducer which is connected to the cell via a 1/16’ nut located at the top-right of the cell. The drainage and liquid injection were performed via an1/8’connnection located at the bottom of the equilibrium cell. The input/output of the gas and liquid were controlled using two ball valves supplied by Swagelok. The cell temperature was measured using a Pt-100 platinum resistance temperature probe located at the top of the cell.
Sealing between the cylinder flange and the cell body was accomplished using an O- ring inserted into the flange and the flange was bolted to the cell body using 6×10 mm stainless steel bolts. The O-ring use must be compatible with the chemicals (refrigerants and SDS) used in the measurements. In this study the most suitable O-ring material was Viton. A schematic diagram of the equilibrium cell is depicted in Figure 5.3. A photograph of the cell body and a schematic diagram of the top view of the cell are presented in Figure 5.4.
Extraction fan
Mechanical overhead stirrer
Aluminium block for pressure transducer Programmable temperature circulator Pt-100
Pump
Isochoric pressure equilibrium cell Mounting for valves
Liquid bath
Figure 5.2. Photograph of the experimental apparatus
60 5.2.2. Hydraulic hand pump
As depicted in Figure 5.1, in this study in order to pressurize the gas inside the high pressure equilibrium cell, distilled deionized water was injected to the cell using a WIKA HD- 250 hydraulic hand pump.
5.2.3. Agitation of the cell contents
As mentioned in chapter 2, agitation of the system increases the rate for gas hydrate formation significantly. Hence, in this study strong agitation of the system was provided. The agitation system consisted of a Heidolph RZR 2041 motor (mechanical overhead stirrer in Figure 5.2), a shaft with a strong magnet and a stirrer device with four blades and a gold coated magnet. The mechanical overhead stirrer motor was placed at the top of the cell in order to rotate the shaft. This motor is equipped with two gear speeds of 40 - 400 rpm and 200 - 2000 rpm. A stirrer speed of 600 rpm was used for all experiments.
Stainless steel shaft
Stainless steel bolts Top flange
Pressure transducer line
External magnet Loading line
Impeller
Cylindrical Internal magnet Isochoric pressure cell Drain line
Drain valve Loading valve Pt-100 insert
Bottom flange
Figure5.3. Isometric view and schematic of the used equilibrium cell in this study, Dominique Richon (personal communication).
a
b
61
Figure 5.4. Side and top view of the high pressure equilibrium cell used in this study.
Figure 5.5 shows a photograph of the stirrer device as well as a schematic diagram of the stirring mechanism used in this study. The magnets inside the stirrer device and shaft were made from Neodymium to provide a strong magnetic field. As observed from Figure 5.5, the stirring device consists of four detachable blades to agitate the cell contents. The length, height and width of each blade were 4, 23, and 1 mm, respectively. The agitation system employed in this study is one of the most efficient agitation systems which can provide complete mixing of the gas, liquid and hydrate phases inside the cell resulting in the reduction of the gas hydrate formation /dissociation time compared to the use of a magnetic bar stirring device.
Drain line Loading line
Isochoric pressure equilibrium cell Pt-100 insert
Pressure transducer line O-ring
Bolts holes
Holes for bolts
Pressure transducer line
Pt-100 insert O-ring
Inner isochoric pressure equilibrium cell
Loading and drain lines
62
Figure 5.5. (a) A photograph of the stirrer device used in this study (b) schematic diagram of the stirring mechanism
5.2.4. The liquid thermostatted bath
A thermostatted bath was employed to keep the cell temperature at a constant value (see Figure 5.2). It was constructed from 316 stainless steel with the dimensions of 43×35×26 cm. The bath was filled with 50 mass percent of ethylene glycol aqueous solution which was suitable to operate in the temperature ranges of 263.15 to 323.15 K. The cell was immersed in the bath to prevent heat transfer from the environment to the cell.
Overhead mechanical strirrer
Mechanical shaft
Top flange
External neodymium magnet (Ring)
Impeller blades
Cylindrical neodymium magnet a)
b)
63 5.2.5. Temperature controllers
A TXF200 programmable temperature controller supplied by PolyScience® was used to control the temperature of the bath which was equipped with an immersion circulator pump and an internal temperature probe. It can operate in the temperature range of 243.15 K to 323.15 K. The programmable temperature controller provides an adjustable rate of cooling/heating during hydrate formation/dissociation.
An immersion cooler or cold finger supplied by PolyScience® was used in order to decrease the bath temperature. The cooler consisted of an evaporator, condenser, compressor and throttling valve for cooling of the liquid bath down to 173.15 K.
5.2.6. Temperature Probe
A Pt100 (platinum temperature probe) with ± 0.03 K uncertainty was connected to the cell in order to measure the temperature of the cell. The temperature probe was connected electrically to a 34972A LX Agilent data acquisition system. The temperature was monitored and recorded along the time during the experiment using the data acquisition system.
5.2.7. Pressure Transducer
A WIKA pressure transducer with an accuracy of 0.05% of full scale was utilized to measure the pressure of the cell. The pressure transducer was connected to the body of the cell to measure the pressure of the cell. Using the 34972A LXI Agilent data acquisition system, the cell pressure was electronically recorded and displayed along with time. In order to avoid any possible vapour condensation inside the pressure transmitter, it is housed in an aluminium block with a constant temperature of 313.2 K. This constant temperature is provided by two heating cartridges which are inserted at the top of the aluminium block. Each heating cartridge has an 8 mm outside diameter and 40 mm length. The temperature of the aluminium block was measured with a calibrated 3 mm diameter and 20 mm length class A, 3-wire Pt-100 and controlled by a Shinko ACS-13A digital indicating controller.