Denitrification controller sysline XR 35N

Transcription

1 Technical Information TI 129C/07/e/ Denitrification controller sysline XR 35N Microprocessor-controlled evaluation instrument for denitrification control via the redox potential of the activated sludge Area of application: Elimination of nitrogen compounds in sewage treatment plants with intermittent denitrification Nitrate zero point is detected via redox break point Control of aeration blowers Benefits at a glance: Good discharge values even without expensive on-line measurement Low maintenance requirements and high availability are guaranteed by use of simple measuring technology Configurable for: time control redox min/max control redox break point control Fail-safe control design Optimised control thanks to parameter sets switchable externally Plain-text operator guidance Several displays provide information on current control statuses and measured values

2 Measuring and control system XR 35N O2 Rx * = Parameter switching Y Blower * measurement O2 measurement Activated sludge basin Example of a measuring and control system for nitrogen elimination in activated sludge basins The control system comprises: The Sysline XR 35N A redox measuring system with a standard signal output (e.g., ma) An oxygen concentration measuring system (recommended) Blowers for oxygen transfer An external switching unit for operation-optimised parameter sets (e.g., preselector, timer) if necessary Process description Nitrogen compounds (ammonium, nitrite, nitrate) in sewage treatment plants are eliminated almost exclusively by means of biological processes. Microorganisms influenced by oxygen transfer decompose the nitrogen compounds into their elemental components, thereby rendering them harmless to the environment. A simple process recommendable particularly for smaller sewage treatment plants is intermittent denitrification. Here, the basin is first aerated (approx mg/l O 2 ), causing nitrification to take place, i.e. the conversion of ammonia nitrogen to nitrate. The aeration is switched off after a defined period of time. When the oxygen dissolved in the activated sludge is used up, the microorganisms change their respiration and are then able to eliminate the nitrate (NO 3 ). This denitrification phase continues until the nitrate is completely consumed, which is indicated by a steep drop in the redox voltage signal. This,,redox break point is detected by the controller. Subsequently the basin is aerated once more, causing the cycle to restart with nitrification. 2

3 Operating modes Timer control The simplest operating mode, particularly important for start-up. The redox and oxygen signals can be recorded to determine the parameters for the other modes of operation. The times for aeration (T b ) and pause (T n ) are adjustable. voltage Aeration max Aeration is switched off when the maximum redox limit is reached. If the limit is not detected, the controller switches off aeration after period T b. The aeration pause can be adjusted as time T n. voltage RxMax Aeration max / min In this mode of operation, the system is controlled via limit values. If the limits are not reached, the underlayed timers (T b, T n ) are used. voltage RxMax Additional function oxygen minimum : The controller stops waiting for the redox potential to reach the minimum limit when the oxygen value drops below a defined limit. Rxmin Aeration break point The aeration phase ends when the maximum redox value is detected or following time T b. Denitrification (pause in aeration) ends 1. when the redox break point is detected, or 2. when a minimum O 2 limit is violated for a defined period of time, or 3. when the pause period (T n ) expires. voltage RxMax Aeration Additional function phosphate elimination : In some sewage treatment plants, a prolonged anaerobic (oxygen-free) phase after completion of nitrate removal may cause "stress" to the microorganisms. This will release phosphate already bound but will also increase phosphate adsorption during the aeration phase. 3

4 Safety As described above, denitrification control is based primarily on the redox potential. The redox voltage is a summary water parameter that is greatly influenced by changes in weather and water composition. For this reason, the Sysline XR35N has been provided with mechanisms that maintain basic operation while at the same time permitting quick adaptation to changing conditions. Fail-safe principle All functions that depend on measured values have an underlayed timer control that takes over in the event a limit value or break point is not detected. This timer safety function can also respond to violations of a minimum oxygen limit. Switchable parameter sets Parameter sets for recurrent events, e.g. rains, summer/winter operation, etc., can be created and stored (up to 5 sets can be stored). These parameter sets include the data for control and measuring signal evaluation, e.g. safety periods, limits, parameters for break point detection, etc. The parameter sets can be activated either on the instrument or via (up to 4) external contacts. Manual operation Automatic program execution stops in the manual mode. The individual program steps can be controlled with the +/ keys. Diagnostics and alarms The diagnosis key provides a quick overview of the current instrument status (e.g., error messages, timer countdown, etc.). The Sysline controller is equipped with five relays: 1 relay for aeration control 1 alarm relay to signal faults in the instrument and ruptured measuring cables ( ma) 3 relays for limit value programming (with pickup delay) by the user Downstream oxygen control During the aeration phase (nitrification), the microorganisms turn ammonium into nitrate. This process requires a high oxygen concentration (approx. 1.5 to 3 mg/l). The bacteria growth can be optimised and power consumption can be significantly reduced by accurate oxygen concentration control during this period. For this purpose, the control system can be extended at any time in a modular fashion by adding a downstream adaptive hybrid controller: XR 35-A44ED XR 35N-A1E Yg1 Y Start/Stop Yg2 Blower Activated sludge basin V2 V1 V3 measurem,ent O2 measurement O2 measurement Example for application: Intermittent nitrogen elimination with oxygen control in the activated sludge basin 4

5 Downstream oxygen control Advantages of downstream oxygen control: Significant energy savings due to: 1. just as much aeration as required 2. special control properties of XR 35 Controller is optimally and automatically adapted to the influencing variables sewage treatment plant loading, oxygen depletion and climatic conditions Free selection of control function: switching (up to 4 blowers) continuous continuous and switching (see example with base load function) During pauses in aeration: Adjustable basic aeration value that is maintained Representative control by integration of 2 oxygen measuring points (mean value computation) Feedforward control is possible Oxygen transfer control with base loads Operation Process info display Bar graph display of redox voltage Sticker indicating physical unit 4 red LEDs for relay switching status indication Manual mode symbol Digital redox voltage display (4 digits) Hinged cover for lower key row Dialogue display for settings The value on the upper line is changed with the +/ keys Display and control elements 5

6 Electrical connection Switching contact 1 Switching contact 2 Switching contact 3 Switching contact 4 Fault sign. contact (closed circuit connection) 1) Power L N PE S AI 1 signal AI 2 Oxygen signal (recommended) Analogue inputs AI 1... AI 2 for current/voltage signal M 1 M 2 SI 1 SI 2 SI 3 SI 4 Voltage sources for meas. Control inputs SI 1... SI 4 transmitter supply (when using 2-wire meas. transmitters) Notes: 1) Contact status shown: no current, fault present Dimensions 72 Cutout for panel mounting: x mm Dimensions of Sysline XR 35N. The unit is intended for panel installation. Panel cutout according to DIN 42700: x mm. The instrument is installed using the supplied fastening elements. 144 Depth of housing: 156 mm, 160 mm with terminal sockets 6

7 Technical data Controller Power supply 230V/115V/100V AC ( %) 50/60 Hz, adjustable via soldering jumper Power consumption 20 VA DC option V DC DC power consumption max. 12 W * External contactors must be fitted with RC protective circuits to manufacturer specifications to prevent contact wear and possible instrument malfunction. Inputs Current Load Voltage Internal resistance Meas. transmitter supply Current limiting Switching inputs Switching outputs* Alarm relay Switching voltage Switching power with ohmic load Relays 1,2 Switching voltage Switching power with ohmic load Relays 3,4 Switching voltage Switching power with ohmic load 0/ ma 50 Ω V 100 kω > 18 V with nominal supply voltage short-circuit proof, limited to approx. 75 ma for connection to floating NO contacts 250 V DC 1 floating NC contact 250 V DC 60 VA, 2 A 1 floating changeover contact per relay, with overvoltage protection for 230 V AC 250 V DC 1000 VA, 4 A 1 floating changeover contact per relay, with overvoltage protection for 230 V AC 250 V 60 VA, 2 A Electrical isolation Supply voltage AC versions Isolation voltage DC versions galvanically separated 3.75 kv no galvanic separation from inputs, only floating measuring signals are to be connected Inputs Input to input no isolation Displays and indicators Process info display voltage Operator display Switching status indication Control elements Membrane keypad on front panel LCD, 45 x 40 mm semi-circular bar graph, 40 segments digital display, 4 digits with sign, height 10 mm liquid crystal dot matrix display 2x16 characters with physical units 1 red LED per relay (not for alarm relay) 3 entry and 3 function keys Ambient conditions Nominal operating range C Storage and transport C Relative humidity % Terminals Standard Optional flat connectors, 2.8 x 0.8 mm, fully insulated removable terminal blocks conductor cross section 2.5 mm 2 7

8 Physical data Physical data Dimensions Front Mounting cutout Mounting depth Weight 72 x 144 mm 68 x 138 mm 156 mm without connector 160 mm with connector max. 800 g (DC) max g (AC) Ingress protection Standard IP 30 Optional IP 43 Ordering system Sysline XR 35N denitrification controller Power supply A 230 V 50/60 Hz B 115 V 50/60 Hz D 24 V DC Y Special version Application 1 break point detection 9 Special version Ingress protection / terminals A Ingress protection IP 30 B Ingress protection IP 43 D IP 30, with terminal blocks E IP 43, with terminal blocks Y Special version XR 35N - complete order code Deutschland Österreich Schweiz Techn. Büro Teltow Potsdamer Straße 12 a D Teltow Tel. ( ) Fax. ( ) Techn. Büro Hamburg Am Stadtrand 52 D Hamburg Tel. (0 40) Fax (0 40) Büro Hannover Brehmstraße 13 D Hannover Tel. (05 11) Fax (05 11) Techn. Büro Ratingen Eisenhüttenstraße 12 D Ratingen Tel. ( ) Fax ( ) Ges.m.b.H Postfach 173 A-1235 Wien Tel. (02 22) Telex Fax (02 22) AG Sternenhofstraße 21 CH-4153 Reinach / Bl 1 Tel. (0 61) Fax (0 61) mwelt uliebe, chlorfrei gebleichtes Papier Der Techn. Büro Frankfurt Eschborner Landstr. 42 D Frankfurt Tel. (0 69) Fax (0 69) Techn. Büro Stuttgart Mittlerer Pfad 4 D Stuttgart Tel. (07 11) Fax (07 11) Techn. Büro München Stettiner Straße 5 D Germering Tel. (0 89) Telex Fax (0 89) Vertriebszentrale Deutschland: Postfach D Weil am Rhein Tel. ( ) Fax ( ) TI 129C/07/e/12.95 Printed in Germany / DT ( )