Optics: measuring and testing – For light transmission or absorption – Of fluent material
Reexamination Certificate
2001-06-14
2003-04-22
Epps, Georgia (Department: 2873)
Optics: measuring and testing
For light transmission or absorption
Of fluent material
C250S343000
Reexamination Certificate
active
06552793
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Applicant claims priority under 35 U.S.C. §119 of German Application No. 199 49 439.8 filed Oct. 14, 1999. Applicant also claims priority under 35 U.S.C. §120 of PCT/DE00/03572 filed Oct. 11, 2000. The international application under PCT article 21(2) was not published in English.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns to a procedure for the photometric determination of the quality of gas, particularly of burning gases, according to the precharacterising part of claim 41.
2. The Prior Art
For determining the quality of gas for example in distribution networks for natural gas or the like, devices for measuring the quality of the guided-through gases are used. These devices measure the condition of gas. Natural gas, because of being a natural product according to its origin and by mixture shows respective fluctuations in respect of its composition, whereas the composition for example of natural gas coming from the different hydrocarbons determines the caloric value from extrapolated quantities. Therefore it is of great importance to measure the guided-through amount of gas in a gas supply network and therewith the respective amount of energy, to determine the exact respective condition at the feeding point into the natural gas network and at the deliverance points of the customers and therewith to deduct a definite transported or supplied amount of energy. In doing so for the customer of the gas, an invoice can always state the actual supplied amount of energy relating to different conditions of the gas and a correspondingly varying amount of energy. Vice versa, the detection of the condition of the gas offers the guarantee for the customer to obtain a desired quality and therewith a required amount of energy.
The determination of the quality of gas obtains additional relevance, since with the elimination of the guiding-through monopoly, the suppliers of natural gas use the same network for delivering gases of quite different provenance and therefore also different composition. Only an easy and cost-effective detection of the condition of the gas by means of cost-effective measuring devices and methods allows for a controllable and accurate accounting.
For the measurement of the quality of gas as relevant quantities, the standard volumetric gross calorific value H
v,n
, the standard density &rgr;
n
and the compressibility coefficient K have to be determined as accurately as possible and also regarding the different gas qualities.
In practice, for the settlement of account, the transported volume Vb of the of the gas at working conditions (pressure p
b
, temperature T
b
) is measured by means of flow measuring devices. With knowledge of the condition of the gas, the compressibility coefficient K can be determined, with which the volume of the gas V
n
at standard conditions (pressure p
n
, temperature T
n
) is calculated.
V
n
=
p
b
T
n
p
n
T
b
1
K
V
b
By means of multiplication of this standard volume with the volumetric gross calorific value H
v,n
at standard conditions, the transported amount of energy Q can be obtained:
Q=V
n
H
v,n
Alternatively, the volume at working conditions V
b
can directly be multiplied with the volumetric gross calorific H
v,b
at working conditions (Energymeter).
Another important quantity for applications with natural gas is the thermal output of gas burners; this varies in accordance to the gas quality and is characterized by means of the so-called Wobbe index Wv: gases with the same Wobbe index Wv deliver the same thermal output at a burner nozzle. For calculating the Wobbe index Wv the standard density &rgr;
n
of the gas is required, from which the relative density according to air is determined (dv=&rgr;gas/&rgr;air)
W
v
=
H
v
d
v
Therefore the determination of the gross calorific value H
v,n
at standard conditions has central relevance for the practical determination of the quality of gas, for example, for accounting purposes.
Until now different devices for the measurement of the gas quality are used. So-called direct and so-called indirect procedures are known. By using direct procedures, the quantities to be determined are measured separately and therefore the gas is transformed to standard conditions, by which expensive treatments of the gas are required.
The gas condition can be determined most easily by means of so-called calorimeters, in which by means of an open flame a gas probe is burnt and submitted to a cooling medium. Heat quantity and the thereupon detectable temperature rise of the cooling medium the calorific value of the burnt gases can be determined. Such devices will need a complicated mechanic for the adjustment of a certain quantitative proportion of gas, combustion air and for example cooling air as cooling medium and are therefore expensive and error prone, and enhanced security requirements for the devices are necessary due to the open burning. Also the maintenance and calibration have to be carried out by qualified personnel, and the calorimeter must be used in conditioned rooms. Therefore the purchase and operating costs of such test assemblies are very high.
Using calorimetry by means of catalytic burning (for example with pellistors) the probe gas is mixed with air and burnt at the 400 to 500° C. hot helixes of a catalyst. The temperature rise of the catalyst is about proportional to calorific value. Because this procedure is based on a sensitive surface effect, it is subject to strong drifts and necessitates frequent calibration with search gas. The catalytic calorimeter is most favorable of all mentioned procedures, however, because it is better suited for control than for accounting because of its accuracy.
The direct measurement of the density &rgr;
b
at working conditions is done with hydrostatic balances, which are very expensive precision devices, with which the buoyancy of a ball filled with nitrogen is measured in accordance to the density of the surrounding medium, here of the probe gas. With another procedure a thin-walled metal cylinder, which is positioned by a current linkage of the probe gas, is set in oscillation. The density of the surrounding gas determines the resonant frequency of the cylinder, which is captured as a sensitive measured quantity. Both procedures are very expensive for the determination of the standard density, because you they require an adjustment to the standard conditions.
The compressibility coefficient K cannot be measured directly, but instead can be calculated by means of different numerical standard-arithmetic techniques out of the directly measurable gas quantities. One of these procedures, the so-called GERG88-procedure (DVGW-worksheet 486) needs the input quantities listed in table 1 below. The amount of substance of CO
2
is determined according to the state of the art by a non dispersive infrared-spectroscopical procedure (NDIR), whereby the gas must be brought into a defined condition near or at standard conditions. The amount of substance of H
2
is of significance only when working with coke oven gases and can be left unattended in the typical natural gases today distributed in Europe. The compressibility coefficient K can be determined to 10
−3
with the help of the GERG88-equation in case of sufficient accuracy of the input quantities.
TABLE 1
input quantities of the GERG88-procedure
P
b
pressure at working conditions
T
b
temperature at working conditions
&rgr;
n
density at standard conditions
H
v,n
volumetric gross calorific at
standard conditions
xCO
2
amount of substance of CO
2
xH
2
amount of substance of H
2
The other procedure for determination of the behavior of real gases is done according to the AGA8-92DC-equation (ISO 12213-2:1997 (E)). This process requires as input quantities the amount of substance of 21 leading gas components (table 2) and has an accuracy of 10
−3
.
TABLE 2
input quantities of the AGA8-92DC-equation
methane
CO
2
ethane
N
2
propane
H
2
S
isobutane
He
n-butane
H
2
O
isopentane
O
2
n-pentane
Ar
n
Collard & Roe P.C.
Epps Georgia
Flowcomp Systemtechnik GmbH
Spector David N.
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