Steam Digest 2002 - CiteSeerX

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Steam Digest 2002 Figure 5: Cross Limiting or Lead-Lag Fuel-Air Ratio Control The MPPC system relies on near identical response from both the air and fuel control loops to prevent fuel rich or air rich mixtutres in the furnace. The difficulty in maintaining this near identical response limits the application of the MPPC system to applications with modest demand swings. Like the Series system, the traditional MPPC system does not have any feedback to the opposing flow controllers, i.e., fuel does not recognize air and air does not recognize fuel. This absence of feedback can result in a combustion imbalance on large or very fast load swings, resulting in either a fuel-rich or lean furnace. To compensate for the lack of feedback found in the MPPC, these systems are normally set-up with additional excess air to over compensate for fuel flow during setpoint excursions, thus maintaining an air-rich furnace on transition. Cross-Limited Metered Control Cross-limited metered parallel positioning control, (a.k.a. cross-limited control (CLC) or leadlag control (LLC)), improves on the MPPC strategy by interlocking the fuel-air ratio control Combustion Control Strategies for Single and Dual Element Power Burners through high and low selectors. This interlock function prevents a fuel-rich furnace by forcing the fuel to follow air flow on a rising demand, and forcing air to follow fuel on a falling demand. The CLC system is a dynamic system, which easily compensates for differences in response times of the fuel and air end devices. This flexibility allows its use in systems that experience sudden and large load swings, as well as very precise control at steady state operation. The CLC operates as follows. In steady state, the steam demand signal, fuel flow and air flow signals to the high and low selectors are equal. Upon a demand increase the low selector applied to the fuel loop forces the fuel flow to follow the lower of either the air flow or steam demand setpoint. Conversely on a falling demand the high selector applied to the air controller forces the air flow to follow the higher or either the fuel flow or demand setpoint. This high/low selector function insures that the burner transitions are always air rich/fuel lean thus preventing a fuel rich furnace environment. 33
Combustion Control Strategies for Single and Dual Element Power Burners 34 The cross-limited control system can easily maintain excess oxygen levels in gas burners to 3-4 percent and 2.5-3 percent in No. 2 oil systems. Additionally, since fuel flow cannot increase (crosslimited) until air flow has begun to increase, fuel cannot overshoot air flow. The use of an oxygen trim system is then incorporated to adjust the excess oxygen levels down to 2-2.5 percent during steady state operation. Because of the CLC system’s capability for close tolerance control, it is suited for all sizes of boilers, which can support the systems cost economically. Additionally the CLC system is readily adapted to oxygen trim control as well as being suited for low NO X burner applications. REFERENCES 1. Mark’s Engineering Handbook, 7th Edition. 2. American Gas Association Research Report 1509. 3. Honeywell Industrial Controls. 4. David. C. Fathing’s, “TechStuff”, www.federalcorp.com. 5. Jack Schilling, Honeywell Peer-Review. Steam Digest 2002
Page 1 and 2: A compendium of articles on the tec
Page 4 and 5: TABLE OF CONTENTS INTRODUCTION Chri
Page 6: CLOSED-LOOP ENERGY MANAGEMENT CONTR
Page 10 and 11: Steam Digest 2002 Energy Efficiency
Page 12 and 13: Steam Digest 2002 Crude oil is refi
Page 14 and 15: Steam Digest 2002 to be newer and h
Page 16 and 17: Steam Digest 2002 Condensing steam
Page 18 and 19: Steam Digest 2002 this case, it is
Page 20 and 21: Steam Digest 2002 Appendix Appendix
Page 22 and 23: Steam Digest 2002 Decision Climate
Page 24 and 25: Steam Digest 2002 as summer approac
Page 26: Steam Digest 2002 late quick and ea
Page 29 and 30: An Analysis of Steam Process Heater
Page 31 and 32: An Analysis of Steam Process Heater
Page 34 and 35: Steam Digest 2002 Combustion Contro
Page 36 and 37: Steam Digest 2002 mal efficiency by
Page 40 and 41: Steam Digest 2002 Insulation Improv
Page 42 and 43: Steam Digest 2002 Reduce Fuel Costs
Page 44 and 45: Steam Digest 2002 Safety Issues in
Page 46 and 47: Steam Digest 2002 Steam 1 Component
Page 48 and 49: Steam Digest 2002 The Human Side of
Page 50 and 51: Steam Digest 2002 Preliminary Resul
Page 52 and 53: Steam Digest 2002 Table 2: Estimate
Page 54 and 55: Steam Digest 2002 Table 5: Energy U
Page 56: Steam Digest 2002 Fuel savings, P
Page 59 and 60: Results from the Industrial Assessm
Page 61 and 62: Steam Digest 2002 Results from the
Page 64 and 65: Steam Digest 2002 ProSteam - A Stru
Page 66 and 67: Steam Digest 2002 Figure 1: Typical
Page 68 and 69: Steam Digest 2002 The value of the
Page 70 and 71: Steam Digest 2002 value shown in Fi
Page 72: Steam Digest 2002 Trbn_A3 Three-Sta
Page 75 and 76: Steam System Improvements at Dupont
Page 77 and 78: Steam System Improvements at Dupont
Page 80 and 81: Steam Digest 2002 Closed-Loop Energ
Page 82 and 83: Steam Digest 2002 Figure 3: Advice
Page 84 and 85: Steam Digest 2002 gions. Constraint
Page 86 and 87: Steam Digest 2002 4. Provide overri
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Steam Digest 2002 Operations can id
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An Introduction to Steam Outsourcin
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