Waste heat recovery tower is an important energy recovery and absorption system in the production of sulfuric acid plant, and the accuracy of its acid concentration analyzer is directly related to the recovery efficiency and system operation safety. Therefore, it is very important to find and solve the failure of acid concentration analyzer in time.

This paper will discuss the flange leakage causes and corresponding solutions of acid concentration analyzer of waste heat recovery tower from the following two aspects, in order to provide reference for relevant technical personnel.

1. Leakage cause analysis

The sulfuric acid measured by the waste heat recovery tower is high temperature concentrated sulfuric acid (120~220℃), and the conventional intrusive or externally clamped acid concentration analyzer can not meet the temperature requirements under this condition. Therefore, only a non-contact conductivity sensor (referred to as a sensor) can be selected to measure sulfuric acid concentration.

It works by using two coils, one as a transmitter and the other as a receiver. When the transmitter coil is energized, the sulfuric acid generates an induced current, and the induced current is proportional to the conductivity of the sulfuric acid concentration, and the receiver coil detects the size of the current and calculates the corresponding conductivity of the sulfuric acid concentration. Because high temperature sulfuric acid is highly corrosive and the insulation material cannot withstand high temperatures, the two coils do not contact sulfuric acid. Therefore, the electrode flanges at both ends of the sensor need to be connected to form a conductive circuit.

Sensor structure is shown in Figure 1.

(Figure 1)

The sensor flange must be insulated from the mounting flanges at both ends during use. The insulation bolts used in the field for sensor installation mainly use tetrafluoroethylene or paper as insulation materials, and tetrafluoroethylene is easily softened by high temperature during use, resulting in the original preload loosening (see Figure 2) and flange leakage of sulfuric acid, which affects the work and safety of the sensor. When paper is used as insulation material, the paper insulation pad is damaged due to bolt torque, water and acid fog during use (see Figure 3), and sulfuric acid leakage occurs in the flange, which affects the work and safety of the sensor.

(Figure 2)

(Figure 3)

Data fluctuation after flange acid leakage (Figure 4)

2. Solution

The main cause of sulfuric acid leakage at the flange position of the sensor is that the original configured insulation components will be deformed by high temperature, sulfuric acid corrosion, rain softening and bolt torsion deformation. The sulfuric acid leakage problem of the sensor can only be solved by solving the problem of the above insulation components.

Eli Lilly Technology has developed an insulation component for the sensor based on the required performance and sulfuric acid characteristics to solve the problem of sulfuric acid leakage in the sensor flange. LJ80 high temperature insulation components (see Figure 5) can be applied to the temperature of -40~260℃, with superior insulation, corrosion resistance, torque resistance of engineering plastics as insulation pad, fastening bolts are made of 304 stainless steel, and PTFE corrosion material is sprayed on the surface, to ensure that the high temperature polygonal components are not corrode by dilute sulfuric acid, reduce the conductivity of rain to the sensor. Thus, the sulfuric acid concentration analyzer can be used for a long time without sulfuric acid leakage causing analysis failure, and ensure the safe operation of the device.

LJ80 High temperature insulation Assembly (Figure 5)

Actual installation Figure 1

Actual installation Figure 2

Data fluctuation after the use of insulation components