A SMART TEMPERATURE CONTROL SYSTEM FOR GENERATING HOT WATER BY RECOVERING WASTE HEAT FROM SINTER COOLER

FIELD OF INVENTION:

Design of new temperature control system for hot water generation through waste heat recovery system (WHRS) and selection of equipment/instrument thereof

BACKGROUND OF INVENTION:

Iron ore sinter is a pre-reduced Blast Furnace feed. Sintering process is a typical counter-current gas-solid reaction process. Sinter-making starts with the preparation of raw mix from iron ore fines, fluxes, in-plant dust & spillage fines, solid fuel, return fines, and metallurgical waste generated at integrated steel plant. These materials are mixed and granulated in one or more stages. Water is added in order to assist the raw mix in obtaining optimum permeability by making granules. The mix is charged onto the sinter machine and then ignited from the top. The air being sucked from the bottom through the ignited layer and thus layer by layer sintering proceeds in the vertical direction on sinter strand. After completion of the sintering process, hot sinter cake (at temperature 700-800C) is discharged from the sintering machine. Hot sinter is fed into the sinter cooler to cool down below 100C for easy transportation.

Sinter Plant-3 (SP-3) of Bhilai Steel Plant (BSP) has Circular annular dip rail deep bed type sinter cooler for the cooling of hot sinter cake. Air at normal temperature is blown from the bottom of the cooler grate with the help of air blower/s and passes through the sinter bed in upward direction. The cooler has 2 air blower each having capacity 13,000 m3/min. In the meanwhile sinter cooler is also moving in forward circular direction. Due to the heat transfer between hot sinter mass and air, air is being heated up-to 400C and thus sinter is cooled to <100C. Thus obtained hot air is allowed to go into the environment (except a small portion being utilised earlier as ignition air). In this way a huge amount of heat energy is wasted. Literature says that, the sintering process takes up approximately 10 % of the total energy consumed in an integrated iron and steel works. Waste gas coming out of sinter machine after sintering carries sensible heat to the tune of @ 24% of total heat input in the sintering process. Approximately 31% is contained as sensible heat of sinter cooler exhaust air. The hot air coming out of the sinter cooler posses huge amount of sensible heat which can be utilised in further application within the sinter plant or outside in the integrated iron & steel plants. This reduces the overall energy requirement by burning fossil fuels in the process. In some of the countries, hot air from sinter cooler is being used for production of high pressure super heated steam and high pressure super heated steam is being used for operation of turbines for power generation. Generated power in this way is fulfils the power requirement for operating sinter machines. In some cases, sinter plant becomes a net exporter of electricity with this technique. In India, a power generation unit has been installed at RINL, Vizag with the help of NEDO, Japan.

OBJECTIVE OF THE INVENTION:

To control temperature of hot water produced from waste heat recovery system (WHRS) by utilising sensible heat of hot sinter cooler gases, within a narrow range (90±5deg C) in order to utilize maximum heat energy and at the same time avoid steam formation to ensure safety of operating personals nearby area and to save instruments.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING:

Fig. 1: illustrates the P&I Diagram of WHRS in accordance with the present invention;

DETAIL DESCRIPTION OF THE INVENTION:

The Fig. 1 shows all the major equipments/instruments used for hot water generation and its temperature control within a narrow range (90±5C). Functions and control of all major instruments are described briefly in the below table:

Sr. No. Instrumentation location Type Measurement Control Indication/ Alarm/ safety Remark
1 Process Water Inlet Line to pump ( Across Filter) Differential Pressure Transmitter Differential Pressure - Local and panel indication Differential Pressure Transmitter (DP-01) is installed to indicate process water pressure drop of filter
2 Process Water Pump Suction line Pressure Gauge Pressure - Local Indication Pressure gauges ( PI-02, PI-03) are installed to indicate pressure of process water before pump P-102 (A/B)
3 Process Water Pump discharge line Pressure Gauge Pressure - Local Indication Pressure gauges ( PI-01, PI-04) are installed to indicate pressure of process water After pump P-102 (A/B)
4 Process Water Line before Plate Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauges (P-05) is installed to indicate Process Water inlet pressure of PHE (E-102)
Temperature Transmitter Temperature - Local and Panel Indication Temperature Transmitter (TT-01) is installed to indicate process water Temperatures locally as well as on panel before PHE (E-102)
5 Process Water Line after Plate Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge (PI-06) is installed to indicate Process water pressure of PHE (E-102) outlet
Temperature Transmitter Temperature - Local and Panel Indication with Alarm Temperature Transmitter (TT-02) is installed to indicate process water Temperatures after PHE (E-102) on panel. It will start alarm if temperature of process water goes below 85 °C
Flow Meter Flow - Local and Panel Indication Flow meter (FM-01) is installed to indicate the Process Water flow locally as well as on panel
Pressure Transmitter Pressure Bypass water flow to maintain the line pressure to 12 kg/cm2 Local and Panel Indication, Safety Pressure Transmitter (PT-01) is installed to indicate process water line pressure. This Pressure will be set to 12 kg/cm2. If pressure of process water line started increasing to 12 kg/cm2 it will give signal to three way diverting valve to bypass the flow to pump suction.
6 Circulating Water Line before Plate Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge (PI-11) is installed to indicate circulating Water pressure of PHE (E-102) outlet
Temperature Transmitter Temperature - Local and Panel Indication Temperature Transmitter (TT-03) is installed to indicate circulating Water Temperatures locally as well as on panel before PHE (E-102)
7 Circulating Water Line after Plate Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge (PI-12) is installed to indicate circulating Water pressure of PHE (E-102) outlet
Temperature Transmitter Temperature - Local and Panel Indication Temperature Transmitter (TT-04) is installed to indicate circulating Water Temperatures locally as well as on panel before PHE (E-102)
8 Circulating Water Pump Suction line Pressure Gauge Pressure - Local Indication Pressure gauges ( PI-13, PI-14) are installed to indicate circulating Water pressure before pump P-101 (A/B)
9 Circulating Water Pump Discharge line Pressure Gauge Pressure - Local Indication Pressure gauges ( PI-15, PI-16) are installed to indicate circulating Water pressure After pump P-101 (A/B)
10 Circulating Water Line before Main Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge ( PI-17) is installed to indicate circulating Water pressure before Main Heat Exchanger E-101
11 Circulating Water Line after Main Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge ( PI-18) is installed to indicate circulating Water pressure after Main Heat Exchanger E-101
Temperature Transmitter Temperature Control Hot Gas exhaust damper and MHE (E-101) inlet damper to control the MHE circulating water discharge temperature at 95 °C. based on this temperature dampers will adjust the gas flow through MHE and exhaust these hot gases as per the requirement Local and Panel Indication with Alarm Temperature transmitter (TI-05) is installed to indicate Temperatures of hot circulating water after MHE on panel. Also it will start alarm in case of temperature exceeding above 97 °C or decreasing below 93 °C
Pressure Relief Valve - Pressure of MHE outlet line is 3 kg/cm2 (Max) Pressure relief valve will exhaust the excess pressure in the Line. Safety -
12 Hot Gas Duct before Main Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge ( PI-19) is installed to indicate pressure of hot gas Before Main Heat Exchanger E-101
Temperature Transmitter Temperature - Local and Panel Indication Temperature Transmitter (TT-06) is installed to indicate Hot Gas Temperature locally as well as on panel before MHE (E-101)
MHE Bypass Modulating Damper - Maintaining the flow through MHE (E-101) based on the MHE Circulating water outlet temperature by allowing the hot gases bypass the MHE Control MHE (E-101) Bypass Modulating Damper to control the MHE circulating water discharge temperature at 95 °C. based on this temperature Bypass Modulating Damper will adjust the gas flow through MHE
Exhaust gas Damper - - Safety In case of failure of blower exhaust damper will be opened and the sinter cooler will keep running in normal mode
13 Hot Gas Duct After Main Heat Exchanger Pressure Gauge Pressure - Local Indication Pressure gauge ( PI-20) is installed to indicate pressure of hot gas After Main Heat Exchanger E-101
Temperature Transmitter Temperature - Local and Panel Indication Temperature Transmitter (TT-07) is installed to indicate Hot Gas Temperature locally as well as on panel After MHE (E-101)
Manometers at blower suction & discharge Pressure - Local Indication Manometer are installed to indicate inlet & outlet Static Pressure of blower (B-101)
14 5 KL make up water tank
T-102 Level Transmitter Level The control valve of normal water line (inlet of Softener) will operate based on the high level low Level of tank T-102. For Extra low level of tank will be indicated with alarm Panel Indication and Alarm High Level-90 %, Low Level-40%, Extra Low Level-25%. This high level, low level and Extra Low Level indications are indicated on the panel
15 10 KL Expansion tank
T-101 Level Transmitter Level Pump P-103 A/B operate as ON/OFF based on the high level-90%, low Level-75% of tank. For Extra low level-50% of tank will be indicated with alarm Panel Indication and Alarm LSH-90%,LSL-75%,LSLL-50%. This high level, low level and Extra Low Level indications are indicated on the panel
Pressure Transmitter Pressure Pressure of Tank T-101 is set to 3 kg/cm2 by adjusting the control valve of compressed Air Local and Panel Indication Pressure Transmitter (PT-02) is installed to indicate Tank T-101 pressure. This Pressure will be set to 3 kg/cm2.
Pressure Relief Valve - Pressure of tank T-101 is set to 3 kg/cm2 Pressure relief valve will exhaust the excess pressure in the tank. Safety -
16 Raw Water Inlet Line to Softener Control Valve Flow Valve will get open or closed based on the level of makeup water tank T-102(5 KL) Panel Indication Valve Open / closed Indication on panel
Pressure Gauge Pressure - Local Indication Pressure gauge ( PI-21) is installed to indicate Softener inlet Water pressure
17 Raw Water outlet Line of Softener Pressure Gauge Pressure - Local Indication Pressure gauge ( PI-22) is installed to indicate Softener Outlet Water pressure
18 Soft Water Pump Suction line Pressure Gauge Pressure - Local Indication Pressure gauges ( PI-08, PI-09) are installed to indicate Soft pressure before pump P-103 (A/B)
19 Soft Water Pump Discharge line Pressure Gauge Pressure - Local Indication Pressure gauges ( PI-07, PI-10) are installed to indicate Soft Water pressure After pump P-103 (A/B)

To recover a part of waste heat from sinter cooler off gases and its use in a useful manner, a Waste Heat Recovery System (WHRS) has been conceptualised, designed, installed and commissioned at sinter machine-1 of SP-3, BSP, Bhilai. This system collects waste heat from the top of the sinter cooler, passes through a counter-current shell and tube type heat exchanger and transfers its heat to the soft water (De-Mineralized water). Again the hot soft water passes through a plate type heat exchanger and exchanges its sensible heat to industrial/ process water. Thus, industrial water is heated around 90C and being used in various applications for improving productivity and quality of sinter as well as reducing production cost. Salient features of the WHRS are as follow:

Particulars Hot Air Circulating Water Industrial water
Heat energy recovered 18,92,000 kCal/hr
Mass flow rate (max.) 66,000 Nm3/hr 45 tph 30 tph
Temperature Inlet (max) 250-300 C 95 C 30 C
Temperature Outlet 120 54 C 90 C

The WHR system is capable of heating 30tph industrial water from 30C to the 95 C on continuous basis. The control system of the WHRS is designed in such a way that in any case industrial water temperature cannot go beyond 97C (Multi fold control). If it goes beyond 100 C, there is a chance of steam formation in the water line. Since the line is designed for hot water, the steam thus form may damage the equipment in the line. Also, it may cause harm to the operating people nearby if there are leakages in the line. Some of the identified chances for steam formation in the water line are as follow:
Case I: If the temperature of hot air goes beyond 3000 C (It goes up to 4000C depending upon the process condition of the sinter making)
Case II: If the flow rate of industrial water becomes less than 30 tph (It happens frequently as and when hot water requirement is less)
Case III: If the inlet temperature of industrial water goes beyond 300 C (It goes up to 500 C in the peak summer)

If any of the above situations arrive, the control system of the WHRS takes corrective action without any manual intervention and keeps the final output temperature of the industrial water in the range of 85-950 C. The control system have been designed indigenously and working highly satisfactorily. Several meters & transmitters for temperature, pressure and flow of the media, water level in the tanks, the SCADA system have been incorporated to control and operate the WHRS.

Control Logic of WHRS:
Once the circulating water temperature riches to 94° C the damper (D-101; please refer to annexure -I) starts bypassing the air directly to the chimney to control the temperature of the circulating water and even if the temperature riches to 96° C the damper bypasses total air directly to the chimney. In bypass operation the MHE (Main heat exchanger; shell and tube type) is being bypassed from the circuit and the pressure drop across the circuit is reduced. As per the blower characteristic curve, at lower pressure drop it will give more flow than the rated. To control that, the pressure of the duct is being measured (PT-03) and the blower (B-101) adjusts its speed automatically by VFD to maintain the same pressure throughout the operation. Above this control system, if further temperature of the soft water goes beyond 97C, damper D-102 open fully to vent out hot air to the environment thus allowing minimum air to the WHRS. This way, by controlling soft water temperature within 94-97C, process water temperature is maintained within the range of 90 ±50 C.

If the hot process water requirement is below 30 t/hr, then process water line get pressurized as WHRS delivers @ 30 tph. Pressure transmitter (PT-01) in the process water line senses the same and opens up by-pass line of the three-way control valve in the process water line. A water flow meter has been installed in the process hot water line to measure the final flow rate. Rest of the hot water is re-circulated to the pump. Temperature transmitter (TT-02) senses the final temperature of the process water.

Usefulness of the Invention:
The WHRS recovers sensible heat of waste cooler off gases and generates hot water at narrow temperature range. The system selected at SP-3, BSP can utilise waste heat to the tune of 18,92,000 kCal/hr from waste hot air (which was going to the environment earlier). This sensible heat was used to produce 30 tph hot water within a temperature range of 90±50 C. Smart control system of WHRS controls temperature of water within a narrow range to avoid steam formation in the water line and ensure safety of the operators and equipments.

Industrial Applicability:
Almost all modern sinter pants have sinter cooler of various types to cool hot sinter produced from the sinter machine. During the cooling of sinter, huge amount of hot air is generated. WHRS enables the utilization of ample amount of sensible heat of hot waste air in sensible manner. This reduces the solid fuel requirements of the sintering process and hence the emission of poisonous gases. Smart temperature control system provides reliable and safe operation of WHRS. The present innovation can be used in all SAIL sinter machines as well as non SAIL sinter plants also in India and abroad.

Numerous characteristics and advantages of the invention covered by this document will be set forth in the foregoing description. It will be understood, however, that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the scope of the invention

WE CLAIM:

1. A temperature control system for hot water generation through waste heat recovery system (WHRS) from sinter cooler comprising of :
a differential pressure transmitter (DP-01) configured for indicating process water pressure drop of filter;
at least two pressure gauges ( PI-02, PI-03) installed for indicating pressure of process water before pump P-102 (A/B);
at least two pressure gauges ( PI-01, PI-04) installed for indicating pressure of process water after pump P-102 (A/B);
at least one pressure gauge (P-05) installed for indicating Process Water inlet pressure of PHE (E-102);
a temperature transmitter (TT-01) installed for indicating process water Temperatures locally as well as on panel before PHE (E-102);
a pressure gauge (PI-06) installed for indicating Process water pressure of PHE (E-102) outlet;
a temperature transmitter (TT-02) installed for indicating process water Temperatures after PHE (E-102) on panel;
a flow meter (FM-01) installed for indicating the Process Water flow locally as well as on panel;
a pressure transmitter (PT-01) installed for indicating process water line pressure;
a pressure gauge (PI-11) installed for indicating circulating Water pressure of PHE (E-102) outlet;
a temperature transmitter (TT-03) installed for indicating circulating Water Temperatures locally as well as on panel before PHE (E-102) ;
a pressure gauge (PI-12) installed for indicating circulating Water pressure of PHE (E-102) outlet;
a temperature transmitter (TT-04) installed for indicating circulating Water Temperatures locally as well as on panel before PHE (E-102);
at least two pressure gauges ( PI-13, PI-14) installed for indicating circulating Water pressure before pump P-101 (A/B);
at least two pressure gauges ( PI-15, PI-16) installed for indicating circulating Water pressure After pump P-101 (A/B);
a pressure gauge ( PI-17) installed for indicating circulating Water pressure before Main Heat Exchanger E-101
a pressure gauge ( PI-18) installed for indicating circulating Water pressure after Main Heat Exchanger E-101;
a temperature transmitter (TI-05) installed for indicating Temperatures of hot circulating water after MHE on panel;
a pressure gauge ( PI-19) installed for indicating pressure of hot gas Before Main Heat Exchanger E-101;
a temperature transmitter (TT-06) is installed to indicate Hot Gas Temperature locally as well as on panel before MHE (E-101);
a control MHE (E-101) Bypass Modulating Damper to control the MHE circulating water discharge temperature at 95 °C. based on this temperature Bypass Modulating Damper will adjust the gas flow through MHE ;
a pressure gauge ( PI-20) installed for indicating installed for indicating pressure of hot gas After Main Heat Exchanger E-101;
a temperature transmitter (TT-07) installed for indicating Hot Gas Temperature locally as well as on panel After MHE (E-101);
a manometer installed for indicating inlet & outlet Static Pressure of blower (B-101);
a pressure gauge ( PI-21) installed for indicating softener inlet Water pressure
a pressure gauge ( PI-22) installed for indicating Softener Outlet Water pressure
at least two pressure gauges ( PI-08, PI-09) installed for indicating Soft pressure before pump P-103 (A/B); and
at least two pressure gauges ( PI-07, PI-10) are installed to indicate Soft Water pressure After pump P-103 (A/B).

2. The temperature control system for hot water generation as claimed in claim 1, wherein the said temperature transmitter (TT-02) is configured to start alarm if temperature of process water goes below 85 °C.

3. The temperature control system for hot water generation as claimed in claim 1, wherein the said pressure transmitter (PT-01) installed is set to 12 kg/cm2.

4. The temperature control system for hot water generation as claimed in claim 1, wherein if pressure of process water line started increasing to 12 kg/cm2, the said the said pressure transmitter (PT-01) is configured to give signal to three way diverting valve to bypass the flow to pump suction.

5. The temperature control system for hot water generation as claimed in claim 1, wherein the said temperature transmitter (TI-05) start alarm in case of temperature exceeding above 97 °C or decreasing below 93 °C.

6. The temperature control system for hot water generation as claimed in claim 1, wherein the said Control MHE (E-101) Bypass Modulating Damper is configured such that In case of failure of blower exhaust damper will be opened and the sinter cooler will keep running in normal mode.

7. The temperature control system for hot water generation as claimed in claim 1, wherein the said control valve of normal water line (inlet of Softener) is configured to operate based on the high level low Level of tank T-102 and for extra low level of tank will be indicated with alarm.

8. The temperature control system for hot water generation as claimed in claim 1, wherein the said Panel Indication configured at Alarm for High Level-90 %, Low Level-40%, Extra Low Level-25%.

9. The temperature control system for hot water generation as claimed in claim 1, wherein the said pressure transmitter (PT-02) is set to 3 kg/cm2;
10. The temperature control system for hot water generation as claimed in claim 1, wherein under condition that the circulating water temperature riches to 94° C the damper (D-101; please refer to annexure -I) starts bypassing the air directly to the chimney to control the temperature of the circulating water and even if the temperature riches to 96° C the damper bypasses total air directly to the chimney. In bypass operation the MHE (Main heat exchanger; shell and tube type) is being bypassed from the circuit and the pressure drop across the circuit is reduced.