The composition of special gas delivery system—taking hydrogen sulfide as an example

1. Introduction

Special gases play a crucial role in modern industrial production, and #Hydrogen sulfide#, as a typical special gas, has the characteristics of highly toxic, flammable, explosive, etc. The safety and reliability of its conveying system are directly related to production safety and personnel health. This article will take hydrogen sulfide as an example to introduce in detail the composition, design points and safety protection measures of the special gas conveying system.

2. System composition

2.1 Gas source equipment

Hydrogen sulfide gas is usually stored in the form of a high-pressure cylinder or a container. According to GB 50646-2020 "Technical Standards for Special Gas Systems Engineering", hydrogen sulfide gas should be stored in a special gas cylinder cabinet or gas cylinder rack, and has good ventilation and explosion-proof measures. The gas cylinder cabinet should be equipped with a leakage detection device and an emergency cutoff system to ensure that the gas source can be cut off quickly and alarmed in the event of leakage.

2.2 Purification Equipment

In order to ensure the purity and dryness of the hydrogen sulfide gas, a purification device needs to be installed in the system. It mainly includes filters and dryers to remove impurities and moisture from gases. For occasions where high purity is required, a purifier is also required to further improve the gas purity.

2.3 Conveyor pipeline system

The hydrogen sulfide conveying pipeline system is the core part of the entire conveying system, and its design and material selection directly affect the safety and reliability of the system.

2.3.1 Material selection

According to the search results, the following materials are recommended for hydrogen sulfide conveying pipelines:

1. Allo (y 825 nickel-based alloy: has excellent resistance to sulfide stress cracking (SSC) and corrosion resistance, and is suitable for high temperature and high pressure environments. Its PREN value (appropriate resistance point) ≥31, which can effectively resist the corrosion of hydrogen sulfide.

2.2507 Super Duplex Stainless Steel: Contains high chromium, molybdenum and nitrogen, has good stress corrosion cracking resistance, and is suitable for hydrogen sulfide-containing environment in the oil and gas industry.

2.32 Pipeline Design

The hydrogen sulfide conveying pipeline should be made of seamless steel pipes, and welding or clamping connections should be preferred. The pipeline system should be equipped with necessary valves, pressure gauges, flow statistics and other accessories, and purge and exhaust devices should be installed in appropriate locations. According to GB50646-2020, hydrogen sulfide pipelines adopt independent pipeline systems and must not be shared with other gas pipelines.

2.4 Control and Monitoring System

2.4.1 Pressure control

Pressure control devices such as pressure reducing valves and safety valves should be installed in the system to ensure that the gas pressure in the pipeline is stable within the safe range. The pressure reducing valve should be selected as a special hydrogen sulfide pressure reducing valve, and the material should match the pipe material.

2.4.2 Flow control

According to process requirements, flow control devices, such as mass flow meters, meter valves, etc., are set up to accurately control the flow rate of hydrogen sulfide.

2.4.3 Leak detection and alarm system

The hydrogen sulfide leakage detection system is an important measure to ensure the safety of personnel, mainly including the following types:

1. Electrochemical sensor: fast response speed (≤30S), high sensitivity (0.1PPM), suitable for low concentration detection. However, it requires regular calibration and the life span is generally 2-3 years.

2. Infrared sensor: strong anti-interference ability, long life span (more than 5 years), suitable for high concentration and harsh environments. But it is costly and large in size.

3. Semiconductor sensor: low cost and suitable for qualitative detection, but poor accuracy and stability.

The system should set up detection probes in key positions such as gas cylinders, valve boxes, gas points, etc., and be linked to the alarm system. The alarm threshold should be set to: lower 10ppm and higher 20-50ppm, which complies with the requirements of OSHA and GBZ 2.1-2019.

2.5 Terminal Equipment

At the hydrogen sulfide use point, a special valve box or valve plate should be installed to control the on-off and adjustment of the gas. The valve box should be equipped with a local exhaust device to prevent the accumulation of leaked gas. For flammable and explosive occasions,

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