English (GB)
14
4.1.7 Process description
This section refers to fig.
General information
The number of electrolysis cells in a Selcoperm electrolyser
depends on the SES type:
Figure
shows the PID of the largest system which includes an
electrolyser type SES-45000 with 6 electrolysis cells. The
functional principal described here also applies to smaller
systems with less electrolysis cells.
The soft water for the Selcoperm electrolyser is connected to soft
water inlet (A). The soft water enters the system via shut-off valve
(V0.01) and passes through pressure reducing valve (V0.02) to
ensure a regulated pressure in the system.
The brine supplied by brine dosing station (BDS) is connected to
brine inlet (B) and passes shut-off valve (V0.10). The brine dosing
station (BDS) is usually equipped with 2 brine pumps (DP0.10)
and (DP0.11). Only 1 brine pump is used for production while the
other pump is in standby mode. The system can be configured to
alternate between the 2 pumps each time production is started or
in case the used pump fails. For simplification the following
description only refers to brine pump (DP0.10).
The degassing and storage tank (DST) can optionally be
equipped with a second standby degassing fan (EF4.02). The
system can be configured to alternate between the 2 degassing
fans each time production is started or in case the used fan fails.
For simplification the following description only refers to
degassing fan (EF4.01), which is included in each system as a
standard.
Production process
When the system starts production, degassing fan (EF4.01) on
degassing and storage tank (E4.05) is switched on. Once the
exhaust air flow sensor (4.13) measures the correct flow rate,
solenoid valve (0.05) opens and brine pump (DP0.10) is started.
The soft water passes flow sensor (0.02) and is mixed with the
brine in static mixer (V0.05). The resulting electrolyte passes flow
sensors (1.10, 2.10, 3.10) and adjusting valves (V1.01, V2.01,
V3.01) before it enters the electrolysis cells via 3-way valves
(V1.02, V2.02, V3.02). The level switches (1.09, 2.09, 3.09)
signal to the PLC that the electrolysis cells are filled. As soon as
level switch (4.04) signals to the PLC that the NaClO (sodium
hypochlorite) solution line is filled, the rectifier (REC) switches on
the DC power supply for the cells (C1.1, C1.2, C2.1, C2.2, C3.1,
C3.2) to start the electrolysis. The temperature switches (1.01 -
1.04, 2.01 - 2.04, 3.01 - 3.04) monitor the temperature of the DC
connections on the cells.
The temperature sensor (0.03) monitors the temperature of the
NaClO solution before it passes outlet (V). The NaClO solution
contains a certain amount of hydrogen gas, which is produced as
a by-product in electrolysis. It is led through a horizontal or
slightly upwards inclining line into the degassing and storage tank
(E4.05). Before entering the tank, the NaClO solution passes the
T-piece (TP) to separate the hydrogen gas. The separated
hydrogen gas is immediately diluted with air from degassing fan
(EF4.01) to 25 % of the LEL. The exhaust air is led away through
exhaust air outlet (T) to a safe external discharge point. The
correct air flow in the exhaust air line is monitored by air flow
sensor (4.13). In addition, the frequency converter of the
degassing fan is used to monitor the fan speed.
When the NaClO solution reaches the stop-fill level in the tank
measured by level sensor (4.10), the process is stopped. First,
the DC power supply from the rectifier (REC) to the electrolysis
cells is switched off. Solenoid valve (0.05) stays open, and brine
pump (DP0.10) keeps running to flush the lines and cells with
electrolyte for a few minutes.
After flushing is completed, brine pump (DP0.10) stops and
solenoid valve (0.05) closes. The flow of electrolyte through the
electrolysis cells stops. The degassing fan (EF4.01) stops after a
few minutes. The system switches into "Standby" mode.
Additional monitoring equipment
The gas warning system (H2S) with two hydrogen sensors (5.01,
5.02) measures the concentration of hydrogen at the installation
location. If hydrogen is detected, the gas warning controller (5.00)
sends a signal to the PLC in the control cabinet (CTR) of the
Selcoperm electrolyser to shut down the system.
The level switch (0.01) detects liquid in the Selcoperm
electrolyser housing.
The level switch (4.03) detects liquid in the collecting tray of tank
(E4.05).
Dosing of produced NaClO solution
The NaClO solution can be dosed directly from tank (E4.05) via
solution outlet (U) to the point of application. It is also possible to
pump the NaClO solution from tank (E4.05) into separate storage
tanks.
Sampling
A sample of the NaClO solution can be taken from sample outlet
(X) via sample valve (V0.09). A sample of the electrolyte entering
the electrolysis cells can be taken at sample outlet (Y) via sample
valve (V0.06).
Draining
After the system has been flushed and switched off, it can be
drained via drain outlet (Z) using drain outlet valve (V0.08) and
3-way valves (V1.02, V2.02, V3.02).
Acid cleaning
For acid cleaning of the electrodes within the electrolysis cells, an
external acid cleaning station can be connected to (C). Acid
cleaning must be done according to section
.
Operation and supervision
All components and safety functions are monitored and operated
via a multi-colour touchscreen on the Selcoperm electrolyser
(SES). If a fault occurs, the system stops and a message is
displayed on the touchscreen.
SES type
Cells inlcuded
SES-5000, SES-7500
C1.1
SES-10000, SES-15000
C1.1, C1.2
SES-20000, SES-30000
C1.1, C1.2, C2.1, C2.2
SES-45000
all cells as shown in fig.
