Procedure for measuring contents of hydrocarbons in liquids containing such

The present invention concerns a procedure for measuring the contents of hydrocarbons in liquids containing such. The liquid to be measured is conducted to a transparent measuring cuvette or equivalent and the measuring cuvette is irradiated with infrared radiation from a radiation source, and the hydrocarbon content present in the liquid is determined on the basis of the difference in absorption between the liquid together with the hydrocarbon in it and the liquid itself. In the procedure is measured the infrared absorption spectrum of the liquid containing hydrocarbons in a preselected, comparatively wide wavelength range (.lambda..sub.beginning,.lambda..sub.end) having a width exceeding that on which the absorption of the hydrocarbon being examined has an effect. The proper absorption of the liquid in the hydrocarbon's absorption range is determined by calculation with the aid of a spectral part outside said range, whereby the absorption of the hydrocarbon contained in the liquid is obtained on the basis of the difference between said absorptions.

BACKGROUND OF THE INVENTION 
The present invention concerns a procedure for measuring contents of 
hydrocarbons in liquids containing such, in which liquids the main 
component is water and which may in addition to hydrocarbons contain salts 
(seawater) or other dissolved chemicals (industrial emission waters). In 
the procedure, the liquid to be measured is conducted into a transparent 
measuring cuvette which is irradiated with IR radiation from a radiation 
source, and the contact of the hydrocarbon present in the liquid is 
determined on the basis of the attenuation caused by the hydrocarbon in 
the 3.4 to 3.5 .mu.m wavelength range. 
The IR absorption method is commonly used, for instance, in laboratory 
determinations of the oil content of waters. An advantage of the procedure 
is its universal applicability based on the fact that the absorptions of 
different oil types at 3.4 .mu.m wavelength are very close to one another. 
Because of the strong absorption of water, it is however necessary, in 
laboratory measurements, to concentrate the sample before it is measured, 
this being accomplished by extracting the oil in carbon tetrachloride and 
separating from the water the extract thus obtained. As a consequence, the 
procedure is slow and introduces a risk of toxic emissions. 
In a procedure known in the prior art, the absorption of water is 
compensated for by forming, from the sample proper, a reference sample 
from which the oil has been removed. When these two are pumped through the 
cuvette in alternation, the attenuation due to the oil can be measured. In 
order to achieve sufficient measuring accuracy, the differential 
temperature between the samples is equalized prior to the cuvette with the 
aid of a heat exchanger, and for eliminating the differential pressure, 
they are always stopped in the cuvette for the duration of measurement. To 
produce the reference sample, an ultrafilter is employed, which removes, 
on the side of the oil, any solid particles which may occur therein. The 
attenuation caused by these is compensated by using, in addition to the 
measuring wavelength, another wavelength at which the oil effects no 
absorption. The procedure combines the accuracy and reliability of the 
laboratory method and the advantage of high measuring speed. Its 
hydraulics part is, however, still complicated, comprising an ultrafilter, 
a pipe line for the reference sample, pumping means for the reference 
liquid and a heat exchanger. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide an improvement in the measuring 
methods known in the art. A more detailed aim of the invention is to 
provide a procedure in which the sample processing involved in the 
measuring procedure known in the art can be substantially simplified. The 
other aims of the invention, and the advantages to be gained therewith, 
are readable in the disclosure of the invention. 
The aims of the invention are achieved by means of a procedure which is 
mainly characterized in that the infra-red absorption spectrum of the 
liquid containing hydrocarbons is measured in a preselected wavelength 
range of relatively great width, the width of this wavelength range 
exceeding that of the range in which the absorption of the hydrocarbon 
under investigation has an effect, and that the proper absorption of the 
liquid, in the hydrocarbon absorption range, is determined by calculation 
with the aid of the spectral part outside said range, whereby the 
absorption of the hydrocarbon in the liquid is obtained on the basis of 
the difference between said absorptions. 
By the procedure of the invention, numerous remarkable advantages are 
gained. The procedure of the invention allows the hydraulics component 
required in the measurement to be substantially simplified. Hereby, it is 
possible to omit, for instance, the ultrafilter inserted in the liquid 
flow line, the reference liquid pipe line going to the measuring cuvette, 
the reference liquid pumping means required in said pipe line, and the 
heat exchanger.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment of FIG. 1, the measuring apparatus used in the measuring 
procedure of the invention has in general been indicated by reference 
numeral 10. The measuring apparatus 10 comprises a measuring unit part 13 
and a hydraulics part 14, and a control part 15. With the measuring 
apparatus 10 is measured the content of the hydrocarbon, or hydrocarbons, 
present in the liquid flowing in the pipe line 11, e.g. the content of 
oil. The transfer pump and homogenizer in the liquid line 11 are indicated 
by reference numeral 12. 
The measuring unit part 13 comprises an IR source 16, a measuring cuvette 
17 or a corresponding transparent pipe length, a detector unit 18, in FIG. 
1 depicted as a two-channel detector, and a processing and transfer unit 
19 for the measuring signals. 
The hydraulics part 14 comprises a pre-filter 20, a pipe line 21 leading to 
the measuring cuvette 17, sample and flushing valves 22, a heat exchanger 
23, and a pressure transducer 24. By reference numeral 25 is indicated the 
discharge line along which the measured liquid is conducted from the 
measuring cuvette 17 to the liquid line 11. For flushing, pure liquid may 
be used, which is conducted through the valves 22 into the measuring 
cuvette 17. It is possible to use either pure water or a suitable solvent 
for flushing. 
In the measuring system presented in FIG. 1 are indicated by interrupted 
lines the ultrafilter 26 for the reference liquid, the pipe line 27 along 
which the reference liquid is conducted to the measuring cuvette 17, and 
the reference liquid pumping means 28 in the pipe line 27. In the 
procedure of the invention, the hydraulics part 14 can be simplified so 
that the part 23,26,27 and 28 used in the procedures of prior art may be 
omitted altogether. 
In FIG. 2 is presented an advantageous embodiment of the measuring unit 
part 13 presented in FIG. 1. The measurement in accordance with FIG. 2 is 
based on so-called multi-colour measurement. In this embodiment. The IR 
source is indicated by reference numeral 16, the measuring cuvette by 
reference numeral 17 and the pipe line leading to the measuring cuvette by 
reference numeral 21, as in FIG. 1. In the present embodiment, for the 
detector unit is used a multi-channel detector 218, before which has been 
disposed a wavelength band selector means 200. The reference numeral 219 
indicates the measuring signal processing and transmitting unit. It is 
thus understood that, in multi-colour measurement, a wide band source is 
used and the measuring head contains a plurality of parallel channels. It 
is easy to provide four channels with a multi-colour detector (each 
element has separate filters). Even more numerous channels can be 
implemented by using a line of detectors and a dispersive element, such as 
e.g. a grating or prism. 
In FIG. 3 is presented another advantageous embodiment of the measuring 
unit part 13 shown in FIG. 3. This embodiment is based on a so-called 
Fourier spectrometer. In this embodiment, reference numeral 16 indicates 
the IR source, reference numeral 17 the measuring cuvette, and reference 
numeral 21 the pipe line leading to the measuring cuvette 17, as in FIG. 
1. In this embodiment is used a wide-band detector 318, to which the 
radiation in the IR range passing through the measuring cuvette 17 is 
conducted with the aid of a sweep interferometer 300. By reference numeral 
319 is indicated the Fourier transform calculating, and signal transfer 
unit. Thus, in the Fourier spectrometer is used a wide band-source, and a 
central part is the sweeping interferometer. The spectrum is established 
by calculation. 
In FIG. 4 is presented a third advantageous embodiment of the measuring 
unit part 13 shown in FIG. 1. This embodiment is based on a laser 
spectrometer. By reference numeral 17 is indicated the measuring cuvette 
and by reference numeral 21, the pipe line leading to the measuring 
cuvette 17, as in FIG. 1. In this embodiment is used a sweeping laser 
source 416 and, for detector, a wide-band detector 418. The reference 
numeral 419 indicates the measuring signal processing and transfer unit. 
It is thus understood that in the laser spectrometer is used a tunable 
laser source and a wide-band detector. 
The control means 15, presented in FIG. 1, provides the display, process 
controls and alarms. The calculation of measuring results is carried out 
by a microcomputer, whereby real time processing becomes feasible and a 
precise algorithm is obtained e.g. for calculating the absorption of 
water. 
In FIG. 5 is graphically presented the absorption graph for water 
containing oil. The absorption graph of water has been entered as an 
interrupted line. The wavelength range pre-selected in the procedure of 
the invention is entered in FIG. 5 on the interval .lambda..sub.beginning 
to .lambda..sub.end. In FIG. 5 is shown one possibility of selecting the 
measuring wavelengths (4-colour measurement) .lambda..sub.1 =3.30 .mu.m, 
.lambda..sub.2 =3.42 .mu.m, .lambda..sub.3 =3.60 .mu.m and .lambda..sub.4 
=3.75 .mu.m. In the present instance, oil affects the intensity value 
I.sub.sample at wavelength .lambda..sub.2. The intensity value I.sub.ref 
of oil-free water can be determined by calculation from the intensity 
values at wavelengths .lambda..sub.1, .lambda..sub.3 and .lambda..sub.4, 
and the absorption of oil is thus obtained as the difference of the 
intensity values of sample and reference. By using a greater number of 
measuring wavelengths, the accuracy and reliability of the measurements 
can be improved. By sweeping methods it is even possible to determine the 
integral of oilinduced absorption over the wavelength range concerned. 
The procedure of the invention has remarkable advantages. The measurement 
is made directly from the water sample, and no complex arrangements are 
needed for processing the sample. The effect of such substances present in 
the water is eliminated from the measurement which give rise to uniform 
attenuation in the wavelength range in question. Such are, for instance, 
solid particles causing turbidity, and certain salts dissolved in the 
water. It is possible to measure by the procedure, in addition to oil, 
also some other hydrocarbons admixed to water.