SCTI - Boiler Controls

BOILER CONTROLS

Throughout the world there is a growing awareness of the need to
reduce emissions. Whether the focus is on CO2, NOX or just fuel
savings, all industries are facing significant challenges in this area.

Autoflame is recognized as the world leader in combustion management solutions. They were the first in the
world to develop an electronic fuel/air ratio control for burners and have maintained the market leadership
through constant development and innovation. The equipment can be fitted to burners of any design and has
the flexibility to provide a solution to virtually any combustion problem.

Technical Overview

In today's climate, we find ourselves under increasing pressure to burn fossil fuels
more efficiently, keeping within ever decreasing limits.

With the majority of burners, the Mk.8 burner management system is able to achieve
and maintain 82% combustion efficiency on Natural Gas and 86% when firing on 35
seconds/#2 oil. For systems with the Exhaust Gas Analyser now EGA MK8, it is
possible to maintain commissioned values of combustion irrespective of changes in
stack pressure, fuel calorific values or barometric conditions.

1. Micro Modulation fuel air ratio control

To maximise the efficiency of any boiler, two factors are of paramount importance: The

fuel/air ratio and the temperature or pressure of the boiler.

The air to fuel ratio should be kept to a minimum that ensures complete combustion

within

the limitations of the combustion head design. Once these settings are arrived at

they

should be infinitely repeatable to a high degree of accuracy.

The temperature or pressure of the boiler should be monitored by the combustion

system

so that the exact amount of fuel and air are fired to achieve the target value. This

target

should be met at all times, regardless of any load change.

The mechanical systems that have traditionally involved cams and linkages to

characterize

the fuel/air ratio cannot meet the criteria above. At most times, the

inaccuracy of the fuel

input response to the monitored temperature/pressure has

meant that the target value has

been significantly exceeded or fallen short of. The

technology in Autoflame's Micro

Modulation system removes these inaccuracies.

At the heart of the system, the microprocessor M.M. unit has up to four channels to

control

independent servomotors. During commissioning, the relative positions of

these motors

are adjusted to provide an optimum air/fuel ratio throughout the load

index of the burner. A

further two channels on the Mk

& MK 8

M.M. are dedicated for

variable

speed drive, for

instance to control a combustion fan motor, a chain grate or

feed

pumps. Up to four fuel

programmes can be commissioned with each one storing

the

positioning values for all six

channels. It is then possible to switch fuels at the touch

a button whilst maintaining

optimum combustion efficiency for each fuel.

The Autoflame combustion control system achieves "Locked On" near stoichiometric

air fuel mixing throughout the fuel input range of the boiler while maintaining

exact

temperature or pressure target values. The load control incorporates full user variable

P.I.D. control to the required temperature/pressure.

The M.M. unit features touch sensitive keypad data entry, LCD display and LED status

indicators. The angular position of each channel is displayed and the status

function

will display the "required" and "actual" set point, burner firing rate % and the selected

fuel programme. A voltage dividing system monitors each channel's

position, enabling

digitised position information to be encoded into the control module's memory. The

relative positioning of the channels are constantly checked by

the system at the rate of

50 times per second.

2. Integrated burner control

The Mk

M.M. introduced an integrated burner control within the M.M. module, including

user configurable safety times for the burner start-up phases.

An internal flame safeguard controller can use self-check UV sensors, which utilitize a

shutter to perform UV proving without the need to shut off the burner.

Autoflame's

patented Auto Adaptive UV sensor technology is also featured:

A conventional UV Flame Scanner works by applying an AC voltage across the bulb.

In the presence of UV light the bulb discharges electrical pulses or counts. As

the

intensity of the UV light increases so the number of counts increase. On a fully

modulating burner there is a great deal of difference in UV intensity between pilot

flame

and high fire. During pilot the minimum number of counts required to register a flame

is nominally 40, on a high turndown burner at high fire the number of

counts may reach

300. If the UV bulb is exposed to this intensity of UV light for a prolonged period, as little

as three weeks, it fails closed circuit becoming a 'runaway

cell', registering UV light

when none is present.

Autoflame use a DC voltage supply to the UV bulb, controlling the amount of time and

voltage that is applied to the bulb in one cycle. The user can set an optimum

required

count for the application. When the 'Auto adaptive UV software' commences on burner

start-up, the DC voltage applied time and value are set to a maximum,

as a UV count is

registered the voltage applied and time are modulated to reach the optimum 40 count.

Typically for pilot flame the voltage and applied time will be

near maximum to register a

small flame, as the burner moves to high fire the voltage and applied time are

decreased as the intensity of UV light increases. Keeping

the voltage and applied time

to a minimum markedly increases the life of the UV bulb, reducing the downtime and

maintenance costs.

Gas, oil and air pressure sensors provide further burner management and safety

features.

Gas valve proving looks for pressure loss in the valve train before the burner fires.

Pressure supervision monitors the gas, air and oil pressure. The M.M. displays

the on-

line readings alongside the originally commissioned values. Upper and lower

boundaries can be defined by the engineer and, if these limits are exceeded, the

M.M.

will shut the burner down.

A lockout history shows the most recent events when the burner was shutdown by the

M.M. Records include the date and time of the lockout, the function on which the

lockout

occurred and the date and time that the lockout was reset.

3. Additional M.M. controls

Intelligent Boiler Sequencing

I.B.S. is a sequencing option for multi-boiler installations to minimize the number of

boiler/burner units in operation for the given load demand. All M.M.s support I.B.S.

for

hot water and steam boilers (with low pressure steam supported on the Mk

M.M.).

Fuel Flow Metering

All M.M. units an instantaneous fuel flow measurement, with totalized standard on the

generation.

Outside Temperature Compensation (and Night Set Back)

This enables the boiler set point to be varied according to the outside air temperature,

so as the outside ambient temperature drops, the boiler set point can rise. The

night

setback facility allows a reduction to the set point to be activated by a line voltage.

Time Clock (and Reduced Set point option)

For each day of the week, a start and stop times can be set and a mode selected for

the day. In "ON off" mode, the burner modulates to the required set point within

the

start/stop time, it is then switched off outside of this time. In "ON rsp" mode, the burner

modulates to the required set point within the start/stop time, but instead of

switching

off afterwards, it maintains a reduced set point.

Twin Burner Capability

Twin Burner allows to burners to be run at the same time and with equal input. Two

configurations are possible, either (a) both burners always fire together or not at

all or

(b) the two burners can run together but can work independently if necessary.

Low Flame Hold and Hand Operation

These two methods are used to override the normal P.I.D. control. Low flame hold

takes the flame to its minimum value. Hand operation allows the fuel valve to be

positioned by the operator.

Golden Start

Each fuel programme can include an ideal start/ignition position that is not necessary

low flame or part of the standard load index.

F.G.R. Management

When implementing flue gas re-circulation, typically channels 3 or 4 may be used to

control the amount of flue gas fed back. Since it is not good practise to feed back

these

gases when the flue gas is cold, channels driving servo motors and AC drives can be

set initially to "F.G.R. positions". These positions would be held after start-

up, either for

a length of time or until a threshold value is reached.

4. Exhaust Gas Analysis EGA MK7 and combustion trim now available CERT's EPA Approved for 2012.

The inclusion of an E.G.A.

MK 7

system expands the Micro Modulation system to the full M.M.

/E.G.A.

specification. As standard, the E.G.A. sampling unit measures O2,

CO2

and CO

from the

exhaust gases. Optional NO and SO2 sensors can be factory fitted. The

combustion data from

sampling unit is fed back to the M.M. to

calculate and

display the

following variables:

O2 %

CO2 %

CO ppm

NO ppm

SO2 ppm

Exhaust gas temperature

Combustion efficiency

5. Remote monitoring and control

D.T.I. Data Transfer Interface

The Data Transfer Interface (D.T.I.) module is the gateway for communications with the

M.M./E.G.A. system. All M.M. and E.G.A. system modules can be networked

using a

simple two wire data connection. The D.T.I. poles each item on the network

periodically, storing the latest set of information in defined memory addresses for

external source.

Over 150 items of data are acquired by the DTI from the MM/EGA system. The

information available for each MM includes the boiler required and actual set points,

burner firing rate, fuel programme selected and channel's angular positions. Inputs to

the DTI can include remote on/off control of the burners, as well as adjustment

of the

temperature or pressure set-points within a range predefined on the MM.

The Win PC DTI software brings monitoring and control of the boiler house to the PC. A

workstation can be connected directly on-site, up to 1km away via line drives or

remotely via modem.

System alarm conditions can be defined in the DTI and if these are triggered the DTI

can dial out and advise of the situation to a remote PC with printer or a text pager

service.

MM/EGA integration with a building management system is supported with the DTI

using the industry standard Modbus and Johnson Metasys protocols.

I./O. Modules

Up to 10 Analogue and 10 Digital Input/Output units can be linked to the DTI module.

These allow ancillary boiler house equipment to be interfaced into the system.

Each Analogue I/O Module has 6 inputs and 6 outputs. Each input can be configured for

0-10V, 0-20mA or 4-20mA. Each output can be individually configured for 0-

10V or 4-

20mA. Text labels and data ranges can be assigned.

An Analogue I/O Module can be connected to an MM to convert MM data directly into

analogue outputs. Please note that this application may require particular MM and

I/O

software versions and must be specified explicitly when ordering.

Each Digital I/O Module has 16 mains voltage inputs and 8 volt free mains voltage

switches. As with the Analogue module, text labels can be assigned.

The I/O Modules are configurable via a terminal emulation program such as

HyperTerminal or ProComm Plus.

The Autoflame combustion control system achieves "Locked On" near stoichiometric air fuel mixing throughout the fuel input range of the boiler while maintaining exact
temperature or pressure target values. The load control incorporates full user variable P.I.D. control to the required temperature/pressure.