🌿 Hydrogen chloride (gaseous chlorides) in waste gases — manual absorption method

Environment PN-EN 1911

Overview

EN 1911:2010 describes the standard reference method (SRM) with three alternative analytical techniques for determining the content of gaseous chlorides emitted into the atmosphere from ducts and stacks; it replaced the three-part standard EN 1911-1/-2/-3:1998. The components and the requirements of the measuring system are given, as are the performance characteristics with minimum criteria; the standard may be applied as an SRM if the total uncertainty of the method is less than ±30 % relative at the daily emission limit value for incineration plants and large combustion plants (or at the limit value from the regulations for other installations). The method determines the concentration of chlorinated compounds which give Cl⁻ ions in the absorption solution — that is, volatile inorganic chlorides expressed as HCl; it has been checked in field tests at waste incineration plants. It is applied to gases with a concentration of chlorides (as HCl) from 1 to 5000 mg/m³ under standard conditions; the limit values of the directives are expressed in mg HCl/m³ for dry gas at 273 K and 101.3 kPa at the reference O₂ content. In Poland the regulation of the Minister of Climate and Environment on measurements of emissions indicates PN-EN 1911 (or an equivalent instrumental method) as the reference method for HCl.

Method principle

A known volume of waste gases is sampled representatively from the duct or the stack over a specified time at a controlled flow, with a probe of regulated temperature; a filter of regulated temperature removes the dust, and the stream of gas with the gaseous chlorides is passed through a series of gas-washing bottles with an absorption solution (chloride-free water). All the parts upstream of the gas-washing bottles must be of inert materials and heated, in order to avoid cold spots and losses of the highly reactive, soluble HCl; the unheated parts are rinsed. The filtration takes place at a temperature of at least 160 °C and 20 °C above the acid dew point (in the presence of ammonia and chloride salts — 180 °C, in order to avoid the formation of NH₄Cl on the filter), because below 130 °C reactions with calcium and ammonium salts retain the chlorides on the filter and give too low a result. Where there are droplets in the gases (e.g. downstream of a wet scrubber without reheating), isokinetic sampling with a probe with a nozzle and a side line of a constant ratio of the flows is required; without droplets non-isokinetic sampling with a straight probe is permitted at the points resulting from the homogeneity test in accordance with EN 15259. The effectiveness of the absorption ε = q1/(q1 + q2) is checked from the share of the second gas-washing bottle. The chlorides in the solution are determined by one of the techniques of the standard, among others ion chromatography (EN ISO 10304-1) or spectrophotometry with mercury(II) thiocyanate; the result is converted to mg HCl/m³ of dry gas under reference conditions, taking the chemical blank and the field blank into account.

Applications

• Periodic measurements of HCl emissions from waste incineration and co-incineration plants and from large combustion plants (Directives 2000/76/EC, 2001/80/EC; at present 2010/75/EU)
• Chemical installations, cement works, glassworks, plants processing chlorinated plastics
• The reference method for the calibration and the checking of automated HCl analysers (AMS)
• Parallel sampling with HF, SO₂, NH₃ and H₂O in side lines (without H₂O with isokinetic sampling) and with dust with isokinetic sampling
• Measurements for integrated permits and for emission reporting

Key parameters

Standard

Standard number

PN-EN 1911:2011 (EN 1911:2010)

Title (PL)

Emisja ze źródeł stacjonarnych — Oznaczanie stężenia masowego chlorków gazowych wyrażonych jako HCl — Standardowa metoda odniesienia

Title (EN)

Stationary source emissions — Determination of mass concentration of gaseous chlorides expressed as HCl — Standard reference method

Step-by-step procedure

1. Sampling strategy

   Establish the character of the process (continuous, discontinuous), the expected concentration and the averaging time, the need for a grid measurement (in accordance with EN 13284-1) and the homogeneity of the gases in the cross-section (EN 15259 — a test with an HCl analyser or with the surrogate gases O₂/CO₂). Check whether there are droplets in the gases — if so, choose isokinetic sampling.

2. Assembly of the system

   Assemble the heated probe (with a nozzle with isokinetic sampling), the filter of regulated temperature, the heated T-piece and the gas-washing bottles with the absorption solution, the safety bottle, the drying agent, the pump, the flow meter and the gas meter; with isokinetic sampling — the main line and the side line with their own systems for the measurement of the flow. Heat the probe and the filter up to ≥ 160 °C (180 °C in the presence of NH₃).

3. Blanks

   Prepare a chemical blank (unexposed absorption solution with the reagents) and a field blank (the whole procedure without sampling the gas), in order to exclude contamination and to confirm the level of the limit of determination.

4. Sampling

   Sample a known volume of gas at a controlled flow over the established time; with isokinetic sampling maintain a constant ratio of the flows of the main line and of the side line. After the end rinse the unheated parts with chloride-free water and add the rinsings to the sample; record the volume, the temperature and the pressure of the gas.

5. Analysis

   Determine the chlorides in the solutions from each gas-washing bottle separately by the chosen technique (ion chromatography in accordance with EN ISO 10304-1 or spectrophotometry with mercury(II) thiocyanate); calculate the effectiveness of the absorption ε = q1/(q1 + q2) and check that the requirements are met.

6. Calculations and test report

   Calculate the mass concentration as HCl in mg/m³ for dry gas at 273 K and 101.3 kPa, convert it to the reference oxygen content; draw up an uncertainty budget (EN ISO 14956, GUM) and a test report in accordance with clause 8 of the standard.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The absorption solutions after sampling contain hydrochloric acid — handling in gloves and goggles; with spectrophotometry with mercury(II) thiocyanate the mercury reagents are toxic, collect the waste separately
• The heated parts of the probe and of the filter (≥ 160 °C) — heat-resistant gloves; work on the stack platform with protection against falling
• The waste gases of incineration plants may contain HCl, HF and SO₂ — use protection of the respiratory tract when opening the ports

Frequently asked questions