BS/EN 14790-2017 pdf download.Stationary source emissions Determination of the water vapour in ducts Standard reference method.
5 Principle
5.1 General
This European Standard describes the standard reference method (SRM) for determining the water- vapour content emitted to atmosphere from ducts and stacks. The specific components and the requirements for the measuring system are described in Clause 6. A number of performance characteristics, together with associated performance criteria are specified for the measurement method (see Table 1 in Clause 7). The expanded uncertainty of the method shall meet the specifications given in this European Standard.
The measurement method described hereafter is appropriate when the flue gas is free of droplets.
Within the scope of this European Standard, it is assumed that gas streams in stacks or ducts are more or less in adiabatic (thermodynamic) equilibrium. In those conditions, droplets can arise only if a gas stream is saturated with water. When no droplets are present in the gas stream, the gas stream is then assumed to be unsaturated with water. A gas sample is extracted at a constant rate from the stack The water vapour of that sample is subsequently trapped by adsorption or by condensation plus adsorption; the mass of the vapour is then determined by weighing the mass gain of the trapping system.
When droplets are present in the gas stream, the implementation of the measurement method described in this European Standard leads to an overestimation of the water vapour content. If the measured value is equal to or higher than the expected value shown in the table in Annex B for saturated conditions at the temperature and pressure of the flue gas, that means that the presence of droplets can lead to biased results; such results shall be rejected.
In such cases, the evidence suggests that the gas stream is saturated with water vapour. Under these conditions, the method is abridged to a determination of the gas temperature. Then, the water vapour concentration is calculated from the theoretical mass of water vapour per unit of standard gas volume at liquid-gas equilibrium, given the actual temperature, pressure and composition of the gas stream.
5.2 Adsorption or condensation/adsorption method
A measured quantity of sampled gas is extracted from the gas stream through a trapping system, which meets the specifications of efficiency (see 8.5.2). The mass gain of the trapping system is measured in order to determine the mass or the volume water vapour content, on the basis of the volume sampled.
5.3 Temperature method
This method applies when gases are water saturated.
A temperature probe is placed in the gas stream saturated with water vapour, until it reaches equilibrium. The amount of water vapour present in the gas is subsequently derived from the temperature, using a water liquid-gas equilibrium chart or table (see Annex B).
A known volume of flue gas is extracted representatively from a duct or chimney during a certain period of time at a controlled flow rate. A filter removes the dust in the sampled volume; thereafter the gas stream is passed through a trapping system. It is important that all parts of the sampling equipment upstream of the trapping system are heated and that the components shall not react with or absorb water vapour (e.g. stainless steel, borosilicate glass, quartz glass, PTFE or titanium are suitable materials).
An example of suitable sampling trains is shown in Annex C. The user can choose between a trapping system made up with either:
— adsorption system (Figure C.1) or
— condensation and adsorption system (Figure C.2).
The choice shall be made to fulfil the efficiency that is required in 8.5.2.
6.2 Sampling probe
In order to reach the measurement points of the measurement plane, probes of different lengths and inner diameters may be used. The design and configuration of the probe used shall ensure the residence time of the sample gas within the probe is minimised in order to reduce the response time of the measuring system.
NOTE 1 The probe can be marked before sampling in order to demonstrate that the measurement points in the measurement plane have been reached.
The sampling probe shall be surrounded by a heating jacket capable of producing a controlled temperature of at least 120 °C and 20 °C higher than the (acid) dew point of gases and shall be protected and positioned using an outer tube.
NOTE 2 It Is possible to perform the sampling of S02 and water vapour simultaneously with the same probe (without nozzle providing no droplets are present).
NOTE 3 It is possible to perform the sampling of 1-ICI and water vapour simultaneously with the same probe (without nozzle providing no droplets are present).
6.3 Filter housing
The filter housing shall be made of materials inert to water vapour and shall have the possibility to be connected with the probe thereby avoiding leaks.
The filter housing may be located either:BS/EN 14790-2017 pdf download.