Overview of solutions
Integrated underground city pipe gallery One tunnel is constructed underground in city to integrate electric power, communication, fuel gas, heat supply, water supply and drainage and various engineering pipelines, with the access hole, hoisting hole and monitoring system with gate, for uniform planning, design, construction and management. It is the important infrastructure and “life line” for guaranteeing city operation.
Fire compartment of underground pipe gallery
The integrated pipe gallery includes one fire zone every less than 200m, the fire zones are separated by fire wall and there is class A fireproof door on the wall. When passing through the fire wall, the pipeline shall be provided with wall bushing. Before implementation, the bushing shall be filled with fireproof materials.
There are 1~2 groups of feeder noses in the middle of each fire zone in main trench. The feeder nose can be 6~8m long, depending on the type of pipe type in gallery, for convenience of installation, maintenance and replacement of various pipes.
Provide the access hole within internal diameter of 100cm at two ends of each fire zone and some places of pipe gallery, and equip the access hole with ladder for personnel access. The access hole cover is provided with special lock which can be opened internally and externally.
It is recommended to provide one IO equipment station of 4m×2.5m in each fire zone. For convenience of personnel access, an access hole shall be provided at the top of IO station and connected with the pipe gallery trench through fire door.
Underground pipe gallery gas compartment requirement on combustible gas detection
According to the latest version of Technical Specification for City Integrated Pipe Gallery Engineering, the natural gas pipeline can be incorporated into integrated pipe gallery and its arrangement in the pipe gallery is specified technologically. Based on above design basis, the combustible gas detection system of underground pipe gallery can be designed as follows:
The natural gas pipe compartment includes fire separation every 200m. Each fire zone include 14 (one every 15m) methane combustible gas detectors and 4 flame-proof audible and visual alarms as the combustible gas alarm system.
In the meantime, 5 H2S detectors and 5 O2 detectors (one every 50m) may be provided in environmental system for staged detection of hydrogen sulfide concentration.
For the underground pipe gallery methane combustible gas detector, it is recommended to adopt the anti-poisoning catalytic combustion sensor or laser sensor instead of infrared sensor, because the infrared sensor is susceptible to moisture.
According to the GB50058 requirements on the anti-explosion of explosive gas environment zone 2, the combustible gas detector of natural gas pipe compartment shall have the explosive-proof grade up to Exd IIC T6 and the IP65 protection class.
The combustible gas detector shall be connected with a combustible gas controller which can start ventilation equipment automatically and manually. The combustible gas controller can be provided in each fire zone, or shared by two fire zones or placed in pipe gallery transformer room every 2km for managing the combustible gas detectors of 10 fire zones.
If the combustible gas controller is directly installed in natural gas compartment, the controller is also required to be placed in a flame-proof box to meet Exd IIC flame-proof requirement. It is also allowed to be installed in IO equipment room between two zones.
The gas controller of each fire zone can either be connected to the fire control graphic display unit in control center through optical network or first to the adjacent fire alarm controller and then to the fire control graphic display unit with the fire alarm controller. The fire control graphic display unit can transmit data to the integrated management platform via communication port to complete overall monitoring and display.
The fan starting line of each zone shall also be connected to control center for remote start of the fan in control center.
Connection of underground pipe gallery gas detector
According to current standard requirement, three gases (combustible gas (methane), hydrogen sulfide, oxygen) shall be monitored in integrated compartment and power compartment, and the carbon monoxide (CO) shall also be designed in some pipe gallery. In the integrated pipe gallery, the detectors are mainly provided at vent or inlet/outlet or ground every 50m and connected to RTU or PLC by branching 4-20mA or RS-485 MODBUS.
In the gas pipe gallery, the combustible gas detectors are provided every 15m. The gas detectors are connected with combustible gas detector via bus and the combustible gas controller transmits signal to the centralized fire control graphic display center via optical network.
Selection of Intersense gas detection system in pipe gallery application
Select TRAX20/TRAX30 combustible gas detector (anti-poisoning catalytic sensor) or TRAX20LS laser combustible gas detector for the detection of combustible gas in underground pipe gallery, and TRAX30E toxic gas detector for the detection of hydrogen sulfide and oxygen.
Select GP6010 bus type combustible gas controller as the combustible gas controller of one or two fire zone(s). The controller can be installed in flame-proof cabinet, or placed in pipe gallery or in IO equipment station between two fire zones in pipe gallery. The combustible gas controller can be connected to 14 combustible gas detectors in the fire zone via four buses. The wiring in fire zone is simple and convenient for installation.
GP6010 combustible gas controller of each or every two fire zone(s) can be connected to the combustible gas graphic display unit in monitoring center via double-loop optical network. The graphic display unit can display the working condition and concentration of each gas detector and the real-time concentration curve and gas concentration.
When the natural gas concentration in natural gas pipe compartment exceeds the alarm limit, GP6010 combustible gas controller can start the emergency ventilation equipment of natural gas compartment accident zone and its adjacent zone. The linkage data of GP6010 controllers in different fire zones can share programming.
Each fire zone is provided with 4 HS200 flameproof audible and visual alarms controlled by GP6010 gas controller.
The graphic display unit in monitoring center can transmit data to the centralized management platform for integrated display.
Network communication of Intersense gas detection system pipe gallery
GP6010 combustible gas controller communication network adopts the high-speed optical fiber ring network technology as the independent optical fiber ring network of combustible gas. GP6010 gas controller connects the gas detector of fire zone, integrating local control, data exchange and remote network, to realize the regional and centralized monitoring of gas detectors in pipe gallery.
High transmission rate: Make the best of the high band width of optical fiber communication technology to realize the high transmission rate of 100Mbit/s. It can transmit the concentration of combustible gas to the graphic display unit in monitoring center in a real-time manner.
Far distance: Because the optical fiber transmission loss is very low to extend the communication distance that the ring network length can reach 50km above, the network coverage can meet requirement.
High reliability: The network reliability is improved largely due to the fault-tolerant ring topology and the less signal attenuation, optical fiber transmission media with strong anti-jamming capability and related control equipment. The network system can be restructured in case of fault to ensure its safe operation.
Design basis for underground pipe gallery combustible gas detection system
Code for Design of Automatic Fire Alarm System (GB50116)
Standard for Design of Combustible Gas and Toxic Gas Detection and Alarm for Petrochemical Industry (GB50493)
Code for Design of City Gas Engineering (GB50028)
Code for Design of Electrical Installations in Explosive Atmospheres (GB50058)
Code for Design of Electronic Information System Room (GB50174)
Technical Code for Protection of Building Electronic Information System against Lightning (GB50343)
Standard for Installation and Acceptance of Fire Alarm System (GB50166)
Code for Construction and Quality Acceptance of Automation Instrumentation Engineering (GB50093)
Specification of Prevention and Control on Occupational Hazards in Confined Space (GBZ/T205)
Technical Specification for City Integrated Pipe Gallery Engineering
Draft of Technical Specification for City Integrated Pipe Gallery Monitoring and Alarm System for approval