ABB SCC Gas Preprocessing System Maintenance and Selection Guide

Practical Guide for Maintenance and Selection of ABB SCC Gas Pre treatment System

In the field of modern industrial process control and environmental monitoring, the measurement accuracy and service life of gas analyzers (such as ABB's EL3000 and AO2000 series) depend not only on the performance of the analyzer itself, but also on the gas state before entering the analyzer. The sample gas directly extracted from industrial sites often contains a large amount of dust, moisture, corrosive gases, or has extremely high temperatures and pressures. If it enters the analyzer directly without effective processing, it will not only cause serious distortion of the measurement results, but also result in permanent damage to expensive optical or electrochemical sensors.

The ABB SCC (Sample Gas Conditioning) series gas pretreatment system is designed to address this pain point. As a "protective shield" connecting harsh working conditions and high-precision analyzers, the SCC system processes the sample gas to a perfect state that meets the analyzer's inlet requirements through a series of modular coolers, feed pumps, filters, converters, and control units. For on-site instrument engineers, mastering the hardware architecture, selection boundaries, and on-site maintenance specifications of SCC systems is the key to ensuring the long-term stable operation of the entire analysis system.

Analysis of Core Preprocessing Components: From Cooling to Feeding

The first priority of gas pretreatment is to control humidity (dew point). ABB provides cooling solutions at different levels.

1.1 SCC-C Compressor Style Gas Cooler

SCC-C is the main equipment for handling complex working conditions, especially suitable for high dust, high temperature or high humidity sample gas environments.

Constant dew point control: The factory set sample gas outlet temperature is+3 ° C, and the dew point stability is extremely high. When the ambient temperature changes by 10 ° C or the flow rate changes by 10 l/h, the fluctuation is only ± 0.3 ° C. This provides an extremely stable basic environment for the analyzer.

Multi material heat exchanger: To cope with gases of different corrosives, the heat exchanger is available in three materials: glass, PVDF (polyvinylidene fluoride), and stainless steel. The pressure adaptation range is extremely wide: glass material supports 50-200 kPa (absolute pressure), PVDF supports 50-250 kPa, and the stainless steel high-pressure version supports up to 1 MPa (10 bar). If a peristaltic pump is selected for drainage, the pressure range is usually limited to 50-150 kPa.

Explosion proof and safety certification: This cooler can be equipped with ATEX and CSA explosion-proof versions (applicable to Zone 2 hazardous areas), and meets the strict requirements of the German Federal Emission Control Law (17th BImSchw). It is widely used in environmental monitoring scenarios such as waste incineration or power plants.

1.2 SCC-F and SCC-S sample gas feeding units

The feeding unit is responsible for drawing the sample gas into the system at a constant flow rate.

SCC-F feeding unit: adopts a completely metal free anti-corrosion gas path design, including two independent gas path channels. Each channel is equipped with a rotor flow meter (10-100 l/h) and a needle valve, with a maximum bypass flow rate of 200 l/h. The diaphragm pump can overcome negative pressure and stably deliver the sample gas to the analyzer.

SCC-S Feed Unit: This is a 19 inch rack mounted (4U height) compact solution designed specifically for simple non corrosive gases. Its biggest highlight is the optional Peltier electronic cooler. Compared with compressor type coolers, Peltier has a smaller volume and its outlet dew point is also controlled at+3 ° C, making it particularly suitable for use with EasyLine series analyzers. It can maintain stable cooling performance even at ambient temperatures up to+50 ° C.

Sample gas conversion and common unit configuration

2.1 SCC-K Converter: Solving the Measurement Difficulty of NO2 and Complex Components

In smoke emission monitoring, NO2 is highly soluble in water at room temperature, which can cause pipeline corrosion and measurement loss. The function of SCC-K converter is to reduce NO2 to NO.

Carbon molybdenum catalytic converter: Based on carbon molybdenum catalyst, the reaction temperature ranges from 320 ° C to 360 ° C (depending on the flow rate). The effective conversion rate of the new catalyst is ≥ 95%, and its service life is usually greater than 6 months. Its advantage lies in the ability to replace catalyst filters without the need for tools, greatly reducing maintenance costs.

Quartz glass thermal converter: For more complex applications such as TRS measurement in the pulp and paper industry, H2 conversion of HCl in chlor alkali plants, and oxidation of chlorinated hydrocarbons in PVC plants, SCC-K provides quartz glass reaction tubes with a maximum working temperature of 680 ° C. This model has no consumable parts and a conversion rate of ≥ 99%, but the heating time is relatively long (about 60 minutes).

Attention: The sample gas pressure of SCC-K must be controlled within p-abs ≤ 200 kPa (catalytic type) or 120 kPa (thermal type), and the system pressure drop must be minimal to ensure smooth gas passage.

2.2 SCC-U common unit: the "distribution and control center" of the system

SCC-U is a 19 inch rack mounted (3U) comprehensive power and control chassis designed specifically for small extraction gas analysis systems.

Powerful power distribution capability: It can distribute single-phase power to various equipment such as analyzers, SCC coolers, SCC-K converters, heating sampling probes (such as PFE2/PFE3), heating pipelines (such as TBL01-S), etc.

Temperature control and calibration logic: Equipped with a built-in temperature controller, it can directly control the temperature of the heating filter and heat tracing pipeline. More importantly, it integrates up to 3 solenoid valves for test gas and ambient air, supporting automatic calibration switching at the cooler or probe end. The analyzer communicates with SCC-U through a 15 pin Sub-D interface (X32) to achieve calibration and fault interlocking.

Firewall for hazardous areas and corrosive gases

For situations containing acidic aerosols or in explosive environments, conventional filtration and drainage are no longer sufficient to ensure safety.

Acid Filter: When the SO3 content in the sample gas is greater than 1 mg/m ³ or SO2 is greater than 1000 mg/m ³ (such as flue gas from heavy oil or hard coal combustion), an acid filter must be installed. The borosilicate microfiber filter has a filtration efficiency of 99.99% for particles ≥ 0.1 μ m, effectively intercepting sulfuric acid aerosols and preventing corrosion of the analyzer chamber.

Explosion proof condensate monitoring (CGKW+ER-144A/Ex): The CGKW condensate monitor combines fine filtration and moisture detection functions. When a conductive liquid enters, the electrode will trigger a signal. If used in Zone 1 or Zone 2 hazardous areas, CGKW (must have a stainless steel casing) must be used in conjunction with ER-144A/Ex isolated switch amplifiers. The input of ER-144A/Ex is intrinsically safe (Ex ia), providing a maximum energy limit of 13.1V and 5mA to ensure absolute safety on site.

Flow and alarm monitoring (KFA isolation amplifier): For flow monitors measuring corrosive gases (such as chlorine gas), the accompanying switch signal needs to be connected to the control system through KFA isolation barriers (such as KFA6-SR2-Ex1. W). KFA can not only isolate the dangerous side, but also monitor line disconnection or short circuit. Once an external fault occurs, the red LED on the panel will flash and give an alarm.

Hard specifications for on-site installation and engineering wiring

Even the most advanced hardware can instantly fail if installed improperly. According to engineering practice, the following specifications must be strictly followed:

Rack installation spacing: When installing SCC-U, SCC-K, SCC-S and other equipment in a 19 inch cabinet, at least 1 height unit (1U) of heat dissipation space must be left between the devices. Especially the SCC-K converter, due to its operation at high temperatures of 320 ° C-680 ° C, must always be installed on the top floor of the cabinet to avoid heating up other analytical instruments.

Laying of heat tracing pipeline: The heating sampling pipeline must be laid at a downward slope. It is strictly prohibited to have U-bends or low-lying areas (water bags) in pipelines. Once condensed water accumulates in the pipeline, it will not only cause the dissolution of sample gas components (especially SO2 and NO2), but also cause gas resistance, resulting in a sudden drop in the suction of the diaphragm pump.

Life management of peristaltic pump tubing: Whether it is SCC-C or SCC-S, peristaltic pump tubing for condensate drainage is a vulnerable component. At a running speed of 5 rpm, its lifespan is usually about 5 months. A regular replacement plan should be established on site. Once the pump tube is found to be deformed, aged, or the discharge volume significantly decreases, it should be replaced immediately. Otherwise, if condensed water is sucked into the sample gas path, it will directly damage the analyzer.

Sealing and pressure testing: The airtightness requirements of the entire SCC system are extremely high (usually requiring 5 × 10 ⁻⁶ hPa/s). When connecting PVDF or PTFE pipelines, ensure that the clamp or sealing ring at the joint is securely fastened in place. When using a pressure reducing valve (such as ABB two-stage stainless steel pressure reducing valve), it is recommended to adjust the outlet pressure between 10-150 kPa to match the feeding requirements of the system.

Common troubleshooting and maintenance strategies

Engineers in the "search solution" phase often face emergency situations such as equipment alarms or data drift. The following is a high-frequency troubleshooting checklist for the SCC system:

Phenomenon: The analyzer reading is low or severely lagging.

Troubleshooting: Check if the temperature of the heat tracing pipeline meets the standard (usually set at 120 ° C-180 ° C). Check if the membrane filter is clogged with dust or aerosols (due to excessive pressure drop). Check if the diaphragm of the SCC-F/S feed pump has ruptured, resulting in insufficient pumping volume. For acid filters, observe if the filter element changes color or if the pressure drop exceeds 50 hPa.

Phenomenon: Water ingress or alarm in the analyzer chamber (such as condensate alarm).

Troubleshooting: Immediately check the temperature display of the SCC-C cooler to ensure it is around+3 ° C. Check if the peristaltic pump has stopped running (possibly due to pump tube rupture or motor failure), and check if the condensate collection bottle is full and causing excessive back pressure. If a CGKW condensate water monitor is selected, check if the electrodes are covered by dirt, which may cause false alarms.

Phenomenon: The conversion efficiency of NO2 decreases, and the measured value of NO is low.

Troubleshooting: Check if the heating temperature of the SCC-K converter has reached the set value (such as 320 ° C). If the temperature is normal, it may be due to the failure of the carbon molybdenum catalyst (usually with a lifespan>6 months), and the carbon catalyst kit needs to be replaced. For the thermal converter, check whether there is carbon deposition or blockage in the quartz tube.

Phenomenon: The flowmeter float jumps violently or cannot be adjusted.

Troubleshooting: It may be due to excessive pressure fluctuations in the sample gas at the front end of the feed pump (a stabilizing valve needs to be installed in front of the needle valve), or liquid accumulation in the gas pipeline causing gas flow pulsation. Check if the power supply voltage allocated by SCC-U is stable to avoid interference caused by frequent start stop of solenoid valves.