Foundation fieldbus technology secco 0306

Foundation FieldBus Technology Application in The Ethylene Project of SECCO (900,000 Tons Per Year)

Foundation FieldBus Technology

Application in The Ethylene Project of

SECCO (900,000 Tons Per Year)

(February 28 of 2006)

SECCO

Senior Engineer

1 Summary of SECCO 900,000 tons per year

ethylene project

SECCO 900,000 tons per year ethylene project is a joint-venture which is constructed by SINOPEC, SPC and BP。

This Project is a intergrated petrochemical complex which

owns the largest scale, latest technology, supreme automated system integrated level in the world at present

The gross investment of the project is about $ 2.700 Billions.

All ten plants, public utility and auxiliary factilities of SECCO 900,000 tons ethylene project were put into commercialized operation on Jun 29th of 2005 It indicated the success of adopting FF fieldbus technology in modernized large-scale integrated petrochemical industry factories.

Summary of Automatic Control System

The whole factory consists of 15 satellite control outstations and are

respectively placed in each production plant，public utility and auxiliary

facilities Various kinds of control system cabinets are installed in every

satellite control outstations and a set of operation station with engineering

station is also set up All of these are designed by explosion proof structure level The outmost satellite control outstation is about 2, 500 kilometers away from central control room Signals from all satellite control outstations to

central control room adopt dual-redundant optic-fibre cable for communication The whole factory sets up a central control room The operation and control management of all production plants, public utility and auxiliary factilites are centralized.

The whole factory automatic system includes: DCS/FCS, SIS, FGS, AMS, ADAQ, MMS, EMS, APC, OPT, OTS, CCTV etc.

Central Control Room（3/4 Parts）

The summary of instruments and

devices of SECCO ethylene project:

Field instruments and devcies totalized 54025 units.

FF fieldbus devices have 14375 units which account for 26.6%.

Total loops are 8200.

Total tag numbers are 168,000.

FF fieldbus network segments are 2473 and each of them are averagely connected to 5.8 units FF

fieldbus devices.

2 The advantages of FF fieldbus

FF field bus control system is a kind of plant field network control

system It is a new technology combined by information technology, computer network and control system The advantages are shown as below:

1 FF fieldbus have the attributes of openness and interoperable.

2 FF fieldbus device is intelligent and self defined function.

3 FF fieldbus control function is highly decentralized.

4 FF fieldbus is the totally digitalized technology with high accuracy

and reliability It has established strong foundation for the future

application of digital technology in the control system.

5 FF fieldbus installation materials and communication workload can be greatly reduced.

6 FF fieldbus system provides means for the decreasing devices’ life

1 FF fieldbus have the attributes of

openness and interoperabilty

The key attribute of field bus devices is

interoperability To do this, each fieldbus device

must has a device description (DD) file which

provides description to make the control system or main machine understand the data meaning in the

devices DD file is similar to a device driver As long

as a PC is installed this driver program, it can

recognize and operate the device, such as a printer Fieldbus foundation has provided DD files for all

standard function modules and converter, and

supporters can use them At the same time,

supporters also can add their own characters, such

2 The intelligence of FF fieldbus device

Fieldbus devices with microprocessor placed in the field

devices have the abilities of digital computation and

communication One pair of transmition lines connects to

many sets instruments and transmits many signals in dual

direction If we add the sensor measure, compensation

calculatation, engineering processing and control functions in the fieldbus device, it can also complete basic control

functions.

For FF device, if the measurement range is not to exceed the

sensor maximum measurement range, we only need to

change XD-SCALE and OUT-SCALE in the AI block.

This is much more convenient that the traditional 4-20mA

transmitter which have to use standard signal generator to

change and vertify the range of the transmitter.

The fieldbus control system is a truly distribution

control system such that control functions can be

distributed to the field devices For example the main PID control block can be set in the transmitter and

the secondary loop can be set in the valve positioner

In that case, it can help to reduce the

communication load between DCS and field

instruments, simplify the system architecture,

reduce the virtual communication chains and

improve reliability.

3 High decentralization of the Control

System

4 D igital information technologies have developed rapidly and establish the

foundation for the application of digital technology in the future

Compared with anolog signal, FF digital signal has strong anti-interference ability, high

accuracy, small transmission error and hence it

improves system reliabilty.

With the development of digital technology, a variety of powerful field devices and function

blocks are emerging The whole digitalization of

fieldbus has laid a strong foundation for its

application.

5 Installation materials and

Commission workload savings

The wiring of fieldbus system is simple Design

specifications require that one fieldbus segment can connect maximum of 9-12 fieldbus devices, with

future expansion space left for 3 devices The usage

of instrument cable, marshalling panels, cable trays, and bridges are reduced and wiring checks workload are also reduced When there is a need to increase fieldbus device, we can connect it to the near

segment, both saving investment and decreasing

workload of design and installation It will save

installation cost above 30% according to relevant

typical engineering project experiences

6 Appling Asset Management

System (AMS) to reduce the

equipmets‘ total life cycle costs.

Because FF fieldbus devices have more self dianogsis

capability and failure analysis abilities, these information

can be sent to the control or management systems

Operators can the Asset Management System (AMS) to

monitor the status and the operation conditions of all the

equipment, to dignose problem areas, so as to predict

failures and schedule maintenance work before the actual

failure occurs At the same time we will make plan for

annual maintenance schedule and space parts inventory

according to the information from AMS We do not need to

check adjust valves periodically which requre much time

and cost.

Using Tradition technology cable and connection box

7 FF technology investment analysis

Assume a process plant with the following configuration:

Fieldbus device：2367

Fieldbus segment：526

Average segment loading：4.5unit/Segment

Using FF fieldbus cable and special connection blocks

Type of device and material quantity

Junction box (10-port MagaBlock x 2) 263

Branch cable (each by 45 meters) 106515 meters

Investment comparison between FF

technology and traditional technology

Fieldbus cable using imported cable,

Average segment loading：4.5 units/segment

Fieldbus cable using imported cable，

If we increase the average segment loading to 6 units/segment, unit：10,000 Yuan（RMB）

Item FF technology FF/normal

Fieldbus cable using local made cable

If we increase the average segment loading to 6 units/segment, unit：10,000 Yuan（RMB）

Item FF technology FF/normal

Key factors of adopting field bus technology to

decrease capital investment:

1 Increase segment loading.

2 Use domestic fieldbus cable.

It is biased to think the superiority of fieldbus is cables saving The most important point is actually its

information and intelligence Fieldbus is not an

expensive new technology Both performance

improvement and cost saving are benefits through

3 Introduction of SECCO FF Application

In order to make the design and installation

of fieldbus comply with the standard of

industry's control system (IEC

61158-2:1993 ), SECCO 90, 000 tons per year

ethylene project stipulate the rules for

design , installing and debugging field bus

of FF

1 H1 field bus network segment design

FF bus design should consider total network segment

current load, cable type, arterial length of bus, length of

fieldbus branched, voltage drop and field equipment

quantity, etc.

The nos of FF device that can be added in a segment is

determined by communication loading, power capacity,

address allocation, and impedance of each segment cable, etc

The design can be checked by the use of “Foundation

Fieldbus Segment Design Tool” provided by Emerson

process management company.

1) FF device quantity on each bus network segment

Each fieldbus segment allows at most 12 units of FF devices In

project design we suggest to install 9 units of FF devices on each bus segment (3 units can be added on each bus segment in the

future) According to statistics, in ethylene project, the average

segment loading is 5.8 units/segments.

2) FF cable length

The allowed length of fieldbus cable is :

A type: Single Shielded Twisted Pair (SAT), 0.8mm 2 ( 18#AWG),

Largest distance: 1900 meter.

B type: All Shielded Twisted Pair (SAT), 0.32mm 2 ( 22#AWG),

Largest distance: 1200 meter.

Practically each bus segment should not be longer than 1200 meters Single branch should not be longer than 120 meters when there are 1-12 sets of devices on the bus The length of branches should be as

3) Fieldbus Segment Power Module

(1) Fieldbus Segment Power Module

Redundant, Isolated Power Modulator.

The function of the power modulator is to guarantee the FF

signal (31.25Kbps ) not to be short-circuited

Main power supply should be redundant This power must be

isolate from ground

The power module outputs voltage is 28V, 35mA It can be hot

plugged or pulled without influence to normal operation Power failure signal is hard wired to DCS for failure alarm.

(2) Terminator

„ There are two terminators in each segment, separately

connected to the two ends of segment One is in the FF power

module and the other is in the ends in the field junction box.

„ Because the communicating signal is sent as current signal and accepted as voltage signals, the terminal turn 15-20mA to 0.75-

(3) Junction box in the field:

In order to prevent the bus from moist, the instruments and junction box use the explosion proof sealed cable

connectors We stipulate to use EEx e junction box offered

by MTL company

We used FF terminal block FF device connections Each

terminal block has it short circuit protection with short

circuit indicator This can guarantee that a branch segment does not influence other branch segment in case of short circuit The short circuit protector will limit the electric

current of each branch segment not to exceed 60mA.

(4) Connection of fieldbus cables

„ When connecting with the fieldbus cables on FF field devices, the

shielding wire of the branch cable should be cut off and should use

the insulating strap to wrap it The shielding wire of every segment

should be connected through the ground terminal in the junction box Shielding wire must be grounded in the Marshalling end Any place

should insulate well to prevent the electrostatic induction and low

frequency (50 H Z ) from interfering

„ If the home run cable is a multi-core cable, shielding wires of different segment is not allowed to connect with each other in junction box

(FJB), and shielding wire is not allowed to connect with each together either

„ The armor steel wire of fieldbus cable is required to earth in the field and both ends of cabinet for preventing the thunder and lightning from interfering The theory of both ends to ground is the same as metal

cable bridge brace should be grounded in a distance

(5) The topological structure of fieldbus

Adopt “tree type” layout topological structure on each fieldbus segment

FF Valve Positioner

FF Transmitter

Junction Box

FF Transmitter Fieldbus Segment branches

(6) Principle of assignment of

important devices on fieldbus segment

„ Grade 1 control valve: Only one grade 1 control valve is allowed to connect on each segment This segment only connect with

measure instruments directly related to this control valve.

„ Grade 2 control valve: Only one grade 2 control valve is allowed to connect on each segment The segment may also connect a grade

3 control valve, but do not allow to connect other grade 1 or 2

control valve.

„ Grade 3 control valve: Two grade 3 control valves are allowed to

connect on the same segment The segment may also connect a

grade 3 control valve and a grade 2 one, but do not allow to

connect grade 1 control valve.

„ For some specific equipment, such as the rectifying tower, FF

device related to the reboiler in the bottom and FF device related

to the cooler in the top of the tower should be placed on different segment

„ For some equipment with multi-variables parameters, for example many reactor with multi temperature and pressure points FF

3) About field bus device non-volatile

FF bus parameters have three kinds:

（1） Dynamic data (D) —— refresh regularly and do not need

to write into NVM

（2）Volatile parameter (N) — such as OUT, CAS-IN, RCAS-IN,

these parameters are written once every 1-5 seconds If

parameters writing is too frequently, memory can be written full

in a few months.

（3）Static data (S)— such as H1-LIM, LO-LIM, GAIM, these

parameters are set manually by operator, therefore changing frequency is very miminal

Attenition should be placed to the Volatile Parameter (N) ‘s

writing situation.

2 Fieldbus design and configuration

1) Macro period and control module executing time

„ Macro period of control loop—— the sum of the operation

time that all function modules execute in one control loop and the time for transmitting on the segment is defined as the

macro period of control loop.

„ Macro period of segment——this is determined by macro

periods of all loops and is not added simply because the

executive time of function module can be overlapped while

the communicating time on segment can not overlapped.

The macro period that one segment requires can be

automatically calculated according to a formula.

(1) If PID Block is placed in the valve positioner

The set time of the macro period of a segment (port ) should be greater than calculated time of this segment, for example if the calculated time is 500ms, then the macro period of segment

should be set to one second At this time It will not influence

the operation time in the PID block It will only affect the

sampling time of AI and AO For example scan time in control block is set to1 second, then the data refreshing period is one second, but PID scanning may have run for 2 times.

(2) If PID block is placed in the DCS controller:

The executive time of the controller has influence on PID block execution time The executing time of the controller must be

greater than set time of macro period of a segment It must

include gathering time of the latest data, PID block execution

and AO data transmission to the segment.