Portable Sulphuric Acid Dewpoint Temperature Monitor

Overview

The acid dewpoint of a flue gas is the temperature, at a given pressure, at which any gaseous acid in the flue gas will start to condense into liquid acid.

The fuels used in boilers, such as coal, heavy oil and natural gas, contains S. during the combustion process, S and O₂ form SO₂, and a small amount of SO₂ is converted into SO₃ under catalysis of Fe₂O₃, V₂O₅ and other catalysts. Under normal circumstances, the volume of SO₃ in the boiler flue gas is 1×10-6～50×10-6, and the water vapor is about 10%. When the temperature of the flue gas is below 200°C, SO₃ and the water vapor are completely combined into H₂SO₄ vapor. A small amount of H₂SO4 vapor will significantly increases the acid dew point. When the surface temperature of the boiler heat exchange equipment is lower than the flue gas acid dew point, the H₂SO₄ vapor will condense on the surface to become sulfuric acid solution with a concentration of about 80%, which will adhere to the surface of the heat exchanger and cause acid corrosion. Typical equipment that is prone to corrosion includes air preheaters, induced draft fans and flue walls.

Corrosion of such equipment will result in system shutdown and expensive maintenance, which directly affects the production efficiency of the plant and increases maintenance costs. In addition, the sulfuric acid will also lead to the emission of acid fumes, which will be detrimental to the local environment or surrounding facilities. The advanced combustor manufacturing and combustion control technique has greatly improved the thermal efficiency of boiler. This increase in efficiency is most due to lowering the exhausting gas temperature; however, the lower gas temperature increases the risk of acid content formation.

The WADT 200-II is a portable acid dewpoint temperature detector that will directly, accurately, and reliably measure the acid dewpoint of the flue gas.

Principle

WADT 200- II employs the conductivity sensor technology to monitor the acid dewpoint of the fuel gas. When the probe is inserted into the duct or flue, the probe tip temperature will increase due to the high-temp flue gas. The air valve of the PCU is then slowly opened to cool the probe tip. The condensation will be indicated on the probe surface due to a rise in electrode current through the sensor. When the temperature drops, the condensation on the probe tip will increase. If the flow rate of the cooling air is reduced, the probe temperature will be increased, and the acid will be evaporated off.

Under the acid dewpoint temperature, the deposition rate and evaporation rate become consistent, the readings of the condensation thickness and current are constant, when the readings remain constant, the temperature is the acid dewpoint under such conditions.

Features

•Provide the dedicated gas-collecting hood, especially collecting the gas in order to avoid the interference under some complicated conditions

•Working duration is 8 hours when fully charged

•Monitor the gas temperature, ambient temperature and acid dewpoint at the same time

•Calculate the minimum temperature of the metal tube wall, the acid concentration and the SO₃ concentration

•Portable instrument, easy to use

•Accurate manual control of the flow of the cooling air

•Integrated analog output and integrated diagnosis

•Easy, quick detection and less maintenance

•Equipped with multiple data connectors, easy to output the data

System Components

System Hardware

• Probe ( With the sensor at the top & Telescopic thermocouple)

• Portable control unit

• Cables: PCU CABLE, probe and PCU connecting cables

• Air hose: probe and PCU air hose , PCU air supply pipe

• All the cables and air supply pipe are 3 meters long

WADT 200-II portable PCU consists of three major units:

Power back: WADT 200- II can be used with either internal battery or power supply. Under normal conditions, the battery can last maximum three months when charging once.

Gas circuit: WADT 200-II gas circuit consists of a filter and an air flow control valve. The Air flow control valve can adjust the flow rate of air entering into the meter in order to cool down the probe temperature.

Control unit: The control unit is used for indicating the acid dewpoint temperature, ambient temperature, current, MMT, SO₃, and H₂SO₄ condensation.

System Software

The software setting of WADT 100-II allows the adjustment of parameters. The entry and exit of the menu system is controlled by the keys on the touch screen.

The display has four modes, which are Dials, Trend, Readings and RBU (Rate of build-up).