INDUSTRIAL and SCIENTIFIC

ferential temperature technique to detect

the cloud point temperature of gas oils and

cycle oils which correlates with the ASTM

D97-IP 15 method. Detection is not affected

by the water content or color of the

sample.

The analyzer has CI cloud point temperature

range from -30-F to +55*F (-35-C to +

15°C) and CI repeatability of i-1-F (?r'/2'C).

The sample cloud point temperature is de-

tected on a cyclic basis, the measuring

period depending upon the difference be-

tween the temperature of the incoming

sample ond ifs actual cloud point. A cloud

point trough-picker is built into the analyzer

to facilitate automatic control of ci process.

The analyzer is housed in two lightweight

aluminium explosion-proof boxes suitable

for use in Class 1, Group D hazardous areas.

The left-hand box houses the sample con-

tainer and cooling unit and is provided with

sample ond cooling water connections.

The right-hand box contains electronic com-

ponents. To minimize errors due to ambient

temperature variations, significant compon-

ents are mounted in CI small oven, thermo-

statted at approximately 13O~F (55' C).

Ai\lALYTICAL INSTRUMENTS FOR CONTINUOUS PROCESSES I

PRINCIPLES AND DESCRIPTION OF OPERATION

The instrument has been designed to detect and record the cloud point temperatures of gas oils and cycle oils and the output correlates with the ASTM D97-IP15 results.

The principle of the method is based on the phenomenon that, upon cooling the sample, a crystal lattice is formed and that the forming of this lattice impedes convection currents. The tem,perature at which the lattice structure develops coincides essentially with the temperatures at which a visible cloud appears.

A thermoelectric cooling unit surrounds the sample container, the bottom of which protrudes from the cooling unit. Two thermistors, protruding into the sample at either end of the sample container, are con- nected into the opposite arms of CI Wheatstone Bridge circuit for differential temperature measurement, while a thermocouple located approximately in the center of the sample container meclsures the sample temperature. When the power to the cooling unit is switched on the sample cools and convection currents fall down the walls of the sample container and rise along the axis. The lower thermistor becomes colder than the upper therm,istor and the bridge becomes unbalanced. At the cloud point temperature, or wax precipitation temperature, convection ceases; the lower thermistor no longer receives the cold stream falling from the walls and the upper thermistor no longer receives the relative warmth of the ascending convection stream. On the contrary the upper thermistor is cooled by heat conduction to the cooling unit. The dif- ferential temperature between the two thermistors is suddenly reduced and, when zero, the detector bridge balances and a transistorized Schmiitt trigger operates. The sample temperature, as detected by the therm- ocouple, is then at the cloud point temperature and is indicated on a recording potentiometric millivolt- meter or similar instrument.

The sequence of events during a cycle may be summarized with reference to Fig, 1 as follows:

1. The 3.minute time delay No. 1 is initiated. The two-way solenoid valve is energized so that the sample container is purged by the sample. Power to the cooling unit is isolated during this period.

2. At the end of the delay period, the solenoid valve is de-energized, thus trapping a sample in the container and allowing the sample s+ream to by-pass the sample container. Power is supplied to the cooling unit, the trapped sample begins to cool and time delay No. 2 is initiated. This delay is included to mute the Schmitt trigger for approximately 90 seconds in order that the trigger does not operate at the beginning of the test.

3. At the cloud point temperature the Schmitt trigger operates and time delay No. 3 is initiated

4. After approximately 5 seconds time delays Nos. 1 and 2 reset, then time delay No. 3 n-sets, time delay No. 1 is initiated and the cycle is repeated.

The time required for a complete cycle is about 10 minutes but this period depends on the sample inlet temperature and also on the cloud point tem~perature.

A cloud point trough-picker is built into the analyzer. This enables the instrument to be used for the automatic control of CI process.

The differential temperature technique for cloud point detection is not influenced by the water content or color of the sample and is applicable to any oil which has a wax precipitation temperature provided that its viscosity at this temperature is not greater than about 10 poise.

SAFETY FEATURES

Two safety devices are incorporated in the analyzer. One is a miniature thermostat fixed to one of the heat sinks of the cooling unit and set at approximately 95OF (35°C). The other is a miniature thermostat fixed to the base of the solenoid valve and set to operate should the sample tem,perature reach 140' F (6O'C). Both circuits serve to protect the cooling unit in the event of cooling water failure. When this hap- pens the analyzer will be isolated from the power supply and the sample will by-pass the sample container.

GENERAL SPECIFICATIONS

Cloud point temperature range Repeatability Analysis time

Sample pressure at inlet to sample container

Sample temperature at inlet to sample container

Sam,ple flow rate Ambient temperature Sample filter particle removal rating Materials in contact with sample Recommended installation Utilities: Electrical Cooling Water (Fresh) Sweepstream sample in and out Analyzer output signal -30°F to +55'F (-35°C to +15'C] +-1'F (&%"C] Approximately 10 minutes (depending on cloud point of sample] 20 psig minimum 95 psig maximum At least 50-F (lO'C] above expected cloud point. Maximum temperature of 140-F (bO"C] 200 - 250 ml/min 120°F mctximum (5O'C] 14 micron Stainless steel Overhead weather protection is desirable. 115 A.C. 60 c.p.s. 0.6 KVA 80°F maximum (25'C], 10 gal/hr nominal 1 gal/min. 1. Type J iron-construction thermocouple 2. 115V A.C. to recorder for troughs-picking

Figure 1

COOLING ASSEMBLY

SHMl'Lt VU I \ z

POWER SIGNAL -----

Control Unit -

Sampling Panel