Patent Application
20070266962
In the drawings:
Referring now to the drawings, in which like reference numerals are used to refer to the same or similar elements, the drawings show a gravity feed, natural circulation boiler 10 for an SAGD process using low quality feedwater for carbonatious material recovery, and comprising a steam drum 14 having an inside diameter of about 3 to about 9 feet, a plurality of downcomer pipes 12 connected to the steam drum for discharging water from the stream drum, a furnace 16 having a plurality of individually replaceable membrane wall modules, each module comprising an upper header 21, a membrane roof 26 connected to and sloping downwardly away from the upper header, a membrane wall 24 connected to and descending from the membrane roof by gently curved tubes (e.g. having a radius of curvature of less than about 3 feet), a membrane floor 22 connected to and sloping downwardly from the membrane wall (also by gently curved tubes having a radius of curvature of less than about 3 feet for example), and a lower header 20 connected to the membrane floor, the roof, the wall and the floor together defining a fire box having an inlet end and an outlet end. The preferred sloping of the roof and floor with respect to its respective header is about 2 to 30 degrees to the horizontal, or more preferably about 5 to 15 degrees or about 10 degrees in the illustrated embodiments.
The furnace 16 includes a membrane front wall 28 connected to the upper and lower header and being at the inlet end of the fire box. Means such as metal walled define a windbox 31 upstream of the front wall. One or more burners 30 at the inlet end of the firebox for heating the firebox. A plurality of riser pipes 36 are connected between the steam drum and the upper header for supplying steam to the steam drum when the firebox in heated, the downcomer pipes being connected to the lower header for supplying water from the stream drum under gravity feed so that each module defines a single circuit.
A rear wall screen 32 at the outlet of the firebox is connected between the downcomer pipes 18 and the riser pipes 36 and at least one steam generator bank 33 is downstream of the screen 32 and is also connected between the downcomer pipes and the riser pipes. A stack 42 is connected to the firebox outlet downstream of the bank and an economizer 42 is in the stack. In an alternative embodiment (not shown) the economizer is positioned prior to the stack.
The boiler may include an SCR or selective catalytic reduction module 46 between the firebox outlet and the stack and a transition flue 38 of reducing cross-sectional area is between the firebox outlet and the stack.
To address the issues of appropriate boiler design for an SAGD process, Suncor's review of the alternate boiler technologies resulted in Suncor's issuance of specification SP100-A-100-1 dated 17 Feb. 2004. This specification included a water analysis that has constituent concentrations that exceed ASME guidelines for boiler feedwater. With current drum boiler accepted standards in mind, a risk analysis to indicate the relative risk factors for each constituent at 1000 psig boiler design pressure was performed at B&W Barberton. Following is a summary of this analysis, along with comments.
According to the present invention, feedwater deaeration is expected to purge the volatile fraction of organics from the water, so they are not expected to be present in the boiler feedwater. This will leave only the residual (up to 10 ppm) oil, grease and other nonvolatile organics in the feedwater. Testing indicated that the expected (design) oil and grease concentration in source water into the evaporator is about 10 ppm so that 10 ppm is the maximum oil and grease concentration in the distillate. Steam/water separation in the evaporator will result in non-volatile organics concentrations in the distillate being significant but less, and probably much less, than ppm. The chemical nature of these organics determines their behavior in boilers and determine their effect on boiler serviceability.
The revised silica concentration is also high (beyond recommended feedwater silica limits for most boilers) but tractable. Indicated concentrations for other species are within acceptable limits for most 900 psi boilers. However, because the chloride concentration is high relative to that of other species, care should be taken to avoid conditions that are conducive to under-deposit corrosion.
Risk versus Feedwater Chemistry:
Table 1 above, indicates estimated level of risk associated with different concentrations of common boiler feedwater impurities. Risk levels are defined in terms of the likelihood of problems (1) in boilers with high heat fluxes and high concentration factors and (2) in more conservatively designed boilers with lower heat fluxes and concentration factors. Risk levels are also defined in terms of the level of chemical expertise and technology required to prevent excessive deposition and corrosion.
Definitions:
Low risk limits: Industry wide standard and common operating range for most industrial 900-1000 psi boilers. Acceptable water chemistry can be maintained by industry common practice. Excessive deposition and corrosion generally occur only where there is contamination beyond indicated limits (e.g. caused by condenser leaks, poor startup practice or purifier failures), poor implementation of feedwater and boiler water treatment, or poor boiler operation (e.g. burner misalignment or low drum level);
Medium risk limits: Impunity levels are high but within range of operation for conservatively designed and operated 900-1000 psi boilers at other locations. Assistance of astute and experienced water chemist and state of the art treatment chemicals and practices may be needed to avoid excessive deposition and corrosion. Problems are possible or even probable, but likely to be solvable with appropriate feedwater and boiler water additives and vigilant control.
High risk limits: beyond operating range for most boilers. Probably feasible with conservative boiler design and special water chemistry control measures, but feasibility cannot be assured. Operation in this range requires pushing limits of established water treatment experience and technologies.
Conservative design: Boilers or conservative design with respect to water chemistry have lower maximum local heat fluxes and concentration factors in areas of steam generation. Consequently, maximum deposit formation rates tend to be lower, and thicker deposits can be tolerated with less tendency for under-deposit corrosion and over heat failures.
Conservative design characterisitics include four factors:
(1) moderate maximum local heat flux;
(2) minimized steam/water stratification in horizontal and sloped tubes, accomplished by increased flow to these tubes and/or application of ribbed tubing;
(3) assured flow stability in all circuits over expected range; and
(4) provision for easy acid cleaning, including provision for easy filling, draining and venting.
Basic Design Rules:
Limit furnace heat release (< about 120,000 Btu/hr/ft2) based on known boiler practice;
Minimize local heat flux (burner clearances and heat input/burner (< about 165 MkB/hr));
Reduce FEGT (inlet temperature to Gen. Bank) (about 2400 F);
Maximize circulating velocity and turbulence;
Limit top quality (reduce steam/water stratification);
Short waterwall and Gen. Bank circuits;
Increase tube, header and drum size;
Avoid tight bends;
Ensure flow stability in all circuits over load range;
Provision for easy acid or mechanical cleaning;
Modular construction suitable for truck transport to remote site;
Simple to erect to minimize field labor;
Removable generating bank modules to minimize downtime—simple, easy to repair/replace;
Bottom supported unit; and
Generating capacity 75,000 to 1,000,000 lb/hr of saturated steam at pressures ranging from 600 to 1600 psig operating pressure.
All of these design rules need not be present in all boilers of the present invention since some rules can be optimized to compensate for loosening other rules, however, each boiler of the present invention is enhanced for use as SAGD process boiler with natural circulation designed to operate with sub-ASME feedwater quality for oil sands heavy oil and bitumen recovery or the like, by following as many of the rules as is practical. These design rules cannot be satisfied with existing B&W Industrial boiler technology, specifically PFI or PFT boiler design.
The boiler of the invention is a new natural circulation boiler type that is capable of operating with sub-ASME feedwater quality available from a bitumen recovery SAGD process in the oil sands of Alberta, for example, and, again for example, a 75,000 to 1,000,000 lb/hr unit. The invention is meant to satisfy the market need for such a boiler.
With reference to
The drum 14 is larger in diameter than typically provided for industrial boilers to accommodate possible foaming due to organic contaminants in the feedwater, for example a 6 foot inside diameter (ID) drum is used for the invention (or a steam drum in the range of 3 to 9 feet ID, or preferably 4 to 8 feet ID, or more preferably 5-7 feet ID).
From drum 14, downcomer pipes 12 feed water to the furnace 16 via feeder tubes 18 connecting the downcomers 12 and lower headers 20. The furnace 16 is water-cooled membrane panel construction. An integrated configuration is used such that the floor 22, walls 24 and roof 26 of the furnace are a single water circuit. This reduces the circuit length to reduce chances of internal deposits. The furnace 16 is configured to avoid sloped tubes with shallow angles. In addition, sloped tube lengths are kept to a minimum to avoid steam/water segregation inside the tube. The furnace front wall 28 is a vertical panel of membrane construction and houses the burners 30 and windbox 31. The roof 26, the wall 24 and the floor 22, together defining a firebox having an inlet end at the front wall 28, and an outlet end, burners being at the inlet end of the firebox for heating the firebox.
The lower headers 20 are all provided with access to at least one but preferably multiple drains, e.g. at 50, for draining and cleaning of the water circuits.
The balance of the boiler comprises furnace steam generation surface arranged in three (or more) modules 16a, 16b and 16c (
The steam generation components (furnace and convective surface) are interconnected to the steam drum 14 via risers or riser pipes 36 between the upper headers 21 and the steam drum. This completes the circulation loop. The outer membrane walls of furnace 16 are preferably covered with insulation, e.g. about 3″ to 6″ minimum fiber board, shown at 44 for example.
From the convective surface, the gas travels through a transition flue 38 to an economizer 40 and stack arrangement 42 as in standard industrial boiler. The boiler of
While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | |
|---|---|---|---|
| 60801474 | May 2006 | US |
