US20120023822A1

US20120023822A1 - Method and System for Controlled Gasification

Info

Publication number: US20120023822A1
Application number: US12/845,879
Authority: US
Inventors: Mark Daniel D'Agostini; Christopher O'Neill
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 2010-07-29
Filing date: 2010-07-29
Publication date: 2012-02-02

Abstract

Disclosed is a system and a method of controlled gasification. The method includes introducing a first fuel to a gasifier in a system, introducing a first fuel to a gasifier in a system, generating a product gas by partially oxidizing the first fuel with an oxidizer including oxygen, directing a first portion of the product gas to a process chamber, and selectively introducing a recycled portion of the product gas to the gasifier.

Description

BACKGROUND OF THE INVENTION

The present invention is directed to gasification. More specifically, the present invention relates to a method and system for controlled gasification in a system having product gas recycle.
Most solid fuel gasification systems contain substantial thermal inertia relative to comparable liquid and gaseous fuel systems. Further, gasification of the solid fuel is preceded by heating of the fuel, and this heating requires a significant amount of time, the exact amount depending upon the fuel feed size, porosity, and density, as well as the gasification system design and operating conditions. Moreover, many solid fuel gasification systems, such as fluidized or non-fluidized bed designs, contain large amounts of stored mass (for example, from fuel and ballast material such as sand). The response of solid fuel gasification systems is often sluggish or slow, particularly when a low energy density feedstock with relatively large particle feedstock is employed. Such is often the case, for example, with feedstocks that include biomass, which is rarely amenable to fine pulverization, and frequently has a heating value of less than 10,000 Btu/lb. This sluggishness hampers the ability of solid fuel gasification systems to adequately satisfy the time-varying demand needs of many industrial processes.
Moreover, the mass transport and mixing processes in solid fuel gasification systems are relatively slow and generally more sensitive to changes in flow rate (occurring with changes in operating conditions) than in gaseous-based gasifiers (partial oxidizers) and liquid-based gasifiers. For example, transport gas (or liquid) flows strongly affect solid fuel mixing dynamics in entrained flow gasifiers, and total gas throughput has a major influence on mixing in bed-type solid fuel gasifiers.
One consequence of such mixing limitations is that solid fuel gasification systems can be highly constrained in the degree of turndown that can be achieved in system output (i.e., Btu/hr of syngas) without causing serious degradation and/or instability in gasifier performance. Further, due to the large inertia of solid fuel gasification systems, the true effect of attempting turndown in such systems is typically delayed, sometimes by several minutes or more. This can create a false sense of safety and stability in the mind of system operators, which can ultimately lead to more catastrophic effects. In slagging gasifiers, for example, time-delayed slag solidification can occur on turndown, creating a bottleneck in reactor flows that often results in a complete system shutdown.
The aforementioned limitations on transient response and turndown of solid fuel systems represent technical hurdles in the application of solid fuel gasification systems to dedicated processes, such as boilers and furnaces that must frequently respond to time-varying energy or production demands.
Conventional approaches for addressing these limitations include running the gasifier at constant output in excess of that which is needed for the process and flaring (i.e., waste burning) of surplus syngas. Another approach is to use multiple parallel reactors, each of which can be separately controlled, and yet another approach is the use of back-up fuels such as natural gas or fuel oil that can augment reactor performance during turndown. Shortcomings in these approaches include lower efficiency associated with flaring unused syngas, additional cost and complexity associated with multiple reactors, and relatively high operating cost and/or lack of availability of back-up fuels.
U.S. Pat. No. 4,489,562, which is incorporated by reference in its entirety, describes a method and apparatus for controlling a gasifier that delivers syngas to a boiler for power generation. The method and apparatus fail to address the above-described drawbacks.
What is needed is a system and method capable of dynamic response and turndown of solid fuel gasification that does not suffer from the aforementioned drawbacks.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present disclosure includes a method of controlled gasification. The method includes introducing a first fuel to a gasifier in a system, introducing a first fuel to a gasifier in a system, generating a product gas by partially oxidizing the first fuel with an oxidizer including oxygen, directing a first portion of the product gas to a process chamber, and selectively introducing a recycled portion of the product gas to the gasifier. A quality parameter of the product gas is analyzed, introduction of the oxidizer and the selective introduction of the recycled portion of the product gas is based upon the quality parameter of the product gas stream, and the first fuel includes a solid fuel.
Another aspect of the present disclosure includes a system for controlled gasification. The system includes a gasifier configured to receive a first fuel and generate a product gas by partially oxidizing the first fuel with an oxidizer including oxygen, an analyzer configured to analyze a quality parameter of the product gas, and a controller configured to receive a product gas quality signal and to respond to the product gas quality signal by initiating selective adjustment of one or more of an oxygen flow rate being introduced to the gasifier, a recycled product gas flow rate being introduced to the gasifier, and a flow rate of the first fuel. The system is configured to recycle at least a portion of the product gas to the gasifier, and the first fuel includes solid fuel.
Another aspect of the present disclosure includes a system for controlled gasification. The system includes a gasifier configured to receive a first fuel and generate a product gas by partially oxidizing the first fuel with an oxidizer including oxygen and a controller configured to receive an energy value signal and to initiate an adjustment in a flow rate of the product gas to a process chamber in response to the energy value signal. The system is configured to recycle at least a portion of the product gas to the gasifier, and the first fuel includes solid fuel.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a schematic view of a configuration for a system according to an exemplary embodiment of the disclosure.

FIG. 2 shows a schematic view of a configuration for a system according to an exemplary embodiment of the disclosure.

FIG. 3 shows a diagrammatic view of a control system for controlling a system according to an exemplary embodiment of the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Provided are methods and systems for controlled gasification in response to a quality parameter of a product gas formed by the gasification. Embodiments of the methods and systems, can dynamically adjust to accommodate changes in fuel quality, and/or are not solely dependent upon adjusting secondary fuel sources for responding to changes in furnace demand. Additionally or alternatively, embodiments of the present disclosure are capable of resolving the aforementioned drawbacks.
FIG. 1 shows an exemplary embodiment of a system 100 having a configuration 303 according to the disclosure. The configuration 303 includes a gasifier 300 capable of providing a product gas or synthesis gas (syngas) to a process chamber (for example, a process furnace 102). The process furnace 102 can be any suitable process furnace (for example, a boiler, melting furnace, reheat furnace, gas turbine, reformer, chemical process reactor, or any other suitable process requiring energy input in the form of fuel).
A quality parameter of the product gas is analyzed. The quality parameter can be (or be representative of) composition of the product gas, temperature of the product gas, heating value of the product gas, gasifier temperature, or any other suitable parameter. In one embodiment, product gas composition, heating value, or a combination thereof of the product gas exiting the gasifier 300 is measured in a gas analyzer 317. The gas analyzer 317 can also measure the temperature of the product gas and/or a representative temperature of the gasifier 300 (for example, refractory or slag temperature). Product gas is delivered to the furnace 102 through a flow control valve 307 (or furnace control valve). A portion of product gas (for example, a slip stream) is recycled as recycled product gas (or recycled syngas) to the gasifier 300 upstream of the flow control valve 307. Motive force for the recycled product gas is provided by any suitable mechanism (for example, by a blower 315). In one embodiment, an additional flow control valve 319 (or recycle control valve) is also provided for additional control precision for recycling the recycled product gas.
The gasifier 300 is configured to receive the recycled product gas, a fuel containing solid fuel (for example, a purely solid fuel, a slurry including solid fuel, or any other suitable fuel containing a solid fuel), and an oxidizer containing oxygen. As used herein, except where specified otherwise, the term “oxygen” refers to an O₂content of at least about 30% by volume. Depending upon process parameters of the furnace 102, design of the gasifier 300, and composition of the fuel, additional inputs may include a secondary liquid or gaseous fuel, air, water, or steam, and/or additives (for example, fly ash, compounds containing calcium, compounds containing magnesium, compounds containing silicon, compounds containing aluminum, compounds containing iron, and any combination thereof). The flow rate of the solid fuel is controlled by a fuel control valve 309. The fuel control valve 309 can be any suitable valve for controlling fuel. For example, the fuel control valve 309 can be a rotary valve, a screw, a conveyor, a lock hopper or the like, or combinations thereof. In one embodiment, the oxidant containing oxygen is divided into two or more streams, each with separate control valves 311, 313. For example, in this embodiment, the totality of gasifier oxygen (and/or oxidizer) can be introduced through oxygen control valve 311, and then a portion of the oxygen can be split to enter the gasifier 300 through flow control valve 313 (or diverter control valve). In this embodiment, greater control over the beneficial effect of the recycled product gas operation and control of the gasifier 300 may be achieved.
Similarly, FIG. 2 shows an exemplary embodiment of the system 100 having a configuration 403 according to the disclosure. The configuration 403 includes gasifier 300, process furnace 102, gas analyzer 317, flow control valve 307, blower 315, and additional flow control valve 319. In addition, configuration 403 shown in FIG. 2 shows an oxidant flow control valve 321. In one embodiment, oxygen enrichment in the furnace 102 is included and adjusted by oxidant flow control valve 321. For example, when the quality of the product gas is below a predetermined parameter, oxidant containing oxygen can be supplied to the process furnace 102. This additional supply of oxygen can improve stability, responsiveness, and control of the process furnace 102 operation. In one embodiment, when the solid fuel input to the gasifier 300 has a lower-than-desired heating value, a predetermined amount of oxidant containing oxygen is introduced to the process furnace 102. The introduction of the predetermined amount of oxidant containing oxygen can maintain a flame temperature in the furnace 102 above a predetermined temperature. That is, without the introduction of the predetermined amount of oxidant to the process furnace 102 to aid in combustion of the product gas, the flame temperature and/or stability of combustion within the process furnace 102 is insufficient to meet a desired energy value and/or desired safety standards.
The system 100 disclosed herein is controlled through a control system 305, the functioning of which is based upon the methods, algorithms, and equations described hereinafter. Likewise, the control system 305 can be used for controlling systems having gasifier design including, but not limited to entrained flow or bed-type designs, slagging or non-slagging designs, and/or fluidized or non-fluidized bed designs. The control system 305 can include functionality and system measurement capabilities corresponding to the relationships identified in relation to the process variables as set forth below.
Referring to FIG. 1, the following mass balance for the gasifier 300 is given as:
M _O2-G +M _SF +M _RSG =M _SG (1)
Where M_O2-Grepresents mass flow of oxygen in the oxidant, M_SFrepresents mass flow of solid fuel in the fuel, M_RSGrepresents mass flow of recycled syngas, and M_SGrepresents mass flow of syngas generated. It will be appreciated by those skilled in the art that the mass flow of oxygen M_O2-Gin the oxidant, the mass flow of solid fuel M_SFin the fuel, the mass flow of syngas M_SGin the product gas, the mass flow of recycled syngas M_RSGin the recycled product gas, and the mass flow of syngas delivered to the furnace in the product gas delivered to the furnace M_F(further described below) each can represent a portion or all of the mass flow. For the purposes of this disclosure, such mass flows are assumed to be the entire mass flow. However, it will be further appreciated by those skilled in the art that the methods disclosed herein and operated in conjunction with control system 305 can be applied to systems without mass flows being assumed to be the entire mass flow. Based upon these assumptions, the mass balance among the syngas generated, the recycled syngas, and syngas delivered to the furnace M_Fis:
M _SG −M _RSG =M _F (2)
Combining equations (1) and (2), after rearranging:
M _O2-G +M _SF =M _F (3)
The energy balance for the gasifier 300 is (based upon the assumption of steady flow and no change between specific enthalpy of the recycled syngas entering the gasifier and the product gas):
M _SF *H _SF +M _O2-G *H _O2 +M _RSG *H _SG =M _SG *H _SG +Q _L (4)
Where H represents specific enthalpy (enthalpy per unit mass), H_O2-Grepresents specific enthalpy of oxygen in the oxidant, H_SFrepresents specific enthalpy of solid fuel in the fuel, H_RSGrepresents specific enthalpy of recycled syngas, H_SGrepresents specific enthalpy of syngas generated, and Q_Lis the energy lost from the gasifier 300. The energy balance among syngas generated, the recycled syngas, and the syngas delivered to the furnace is:
M _SG *H _SG −M _RSG *H _SG =M _F *H _SG (5)
The instantaneous energy input to the process furnace, Q_F, is the product of the flow rate of the syngas delivered to the furnace and the heating value. That is:
M _F *H _SG =Q _F (6)
Substituting equation (6) into equation (5):
M _SG *H _SG −M _RSG *H _SG =Q _F (7)
By assuming that the oxygen enthalpy H_O2is equal to zero (which generally indicates that the oxidizer is introduced at a reference temperature, such as 68° F. (20° C.)) and by substituting the relation M_RSG/M_SG=β into equation (4) and rearranging:
M _SF *H _SF =M _SG *H _SG*(1−β)+Q _L (8)
Invoking a similar substitution into equation (7) yields, after rearranging:
Q _F =M _SG *H _SG*(1−β) (9)
Substitution of equation (9) into equation (8) yields the following equality:
M _SF *H _SF =Q _F +Q _L (10)
Finally, combining equations (6) and (10) and eliminating Q_F, yields:
M _SF *H _SF =M _F *H _SG +Q _L (11)
Equation (11) indicates that, under steady flow conditions and assuming constant gasifier energy loss, the energy delivered to the furnace from syngas correlates to the solid fuel energy input to the gasifier. Hence, although the instantaneous energy demand to the furnace 102 can be satisfied by adjustment to the ratio of mass flow rate of recycled syngas to mass flow rate of syngas generated (hence, adjustment of β) as indicated in equation (9), the equality of (11) is eventually established for steady operation by the control system 305.
In one embodiment, the solid fuel in the fuel is assumed to at least consist essentially of carbon, hydrogen, oxygen, nitrogen and water:
Solid Fuel=CH_a1O_a2N_a3 +a ₄H₂O (12)
Where a1, a2, and a3 are the ratios of elemental hydrogen, oxygen, and nitrogen to elemental carbon in the solid fuel, and a4 is the molar ratio of water to fuel carbon. Similarly, the recycled syngas composition (which is assumed to be identical to the product syngas composition as described above) is assumed to consist of carbon monoxide (CO), hydrogen (H₂), methane (CH₄), water vapor (H₂O), carbon dioxide (CO₂) and nitrogen (N₂) according to the following formula:
Syngas=a ₅CO+a ₆CH₄ +a ₇H₂ +a ₈N₂ +a ₉H₂O+a ₁₀CO₂ (13)
Where a₅, a₆, a₇, a₈, a₉and a₁₀are the molar ratios of CO, CH₄, H₂, N₂, H₂O and CO₂to carbon in the solid fuel.
If it is assumed that complete combustion of the solid/gaseous fuel mixture results in the formation of carbon dioxide (CO₂) and water (H₂O) then the molar ratio of oxygen added to carbon in the solid fuel ω_stoichfor stoichiometric (complete, no excess O₂) combustion of the solid fuel/recycled syngas mixture is given as follows:
ω_stoich =n _O2 /n _C=1+0.25*a ₁−0.5*a ₂+0.5*a ₅+2*a ₆+0.5*a ₇ (14)
Where n_O2and n_Care the molar flow rates of oxygen and solid fuel carbon, respectively. The stoichiometric ratio φ is defined herein as the ratio of actual to stoichiometric oxygen injected into the gasifier. While the value of φ will vary depending upon process conditions, gasifier design, and fuel properties. In one embodiment, the range of φ is 0.1 to 0.5.
The actual oxygen flow rate to the gasifier M_O2-G, is equal to:
M _O2-G =M _C*ω_stoich*φ*(MW _O2 /MW _c) (15)
Where M_Cis the mass flow rate of solid fuel carbon to the gasifier, and MW_O2and MW_Care the molecular weights of oxygen and carbon, respectively.
Although the formulae given in equations (1) through (15) assume both compositions and flow rates of solid fuel and recycled syngas are known, measurement of solid fuel composition is an optional input, and can be approximated (for example with periodically obtained data) or eliminated. The latter case is presented in a later example.
In one embodiment, the control system 305 can be operated according to the process set forth in FIG. 3. A difference between a desired energy value D and an output energy value Y (shown as a first comparator step 702) gives rise to an error function c such that:
ε=D−Y (16)
The output energy value Y may include any one or multiple process furnace variables that may be communicated to the controller as an energy value signal whose values or representatives of values are inputted to the first comparator step 702, for example steam temperature, pressure or flow rate, electrical generator output, process furnace temperature, gas flow rate, or any other suitable performance variables, the availability and significance of which depend upon the specific nature of the process furnace (for example, boiler, melting furnace, gas turbine, etc.). The first adjustment step 730 includes such adjustments. For example, based upon the first comparator step 702, the control system 305 may adjust syngas flow (box 704), solid fuel flow (box 706), and/or gasifier oxygen flow (box 708). In one embodiment, a predetermined combination of syngas flow (box 704), solid fuel flow (box 706), and/or gasifier oxygen flow (box 708) is adjusted when the absolute value of E exceeds a predetermined threshold, the magnitude of which is specific to the dynamics and degree of control precision required of the system. The first response of the control system is to the furnace process deviation in order to satisfy the immediate need to reduce the value of the error function ε expediently. This is accomplished through adjustment of the syngas flow rate (box 704) to the process furnace 102, which is enabled via modulation of control valve 307.
In order to re-attain steady operation of the system that is upset by adjusting in syngas flow (box 704), the solid fuel flow rate to the gasifier 300 is adjusted (box 706) by an amount that corresponds to the change in syngas energy flow to the furnace 102. Since adjustments to syngas flow rate (box 704) and adjustments to solid fuel flow rate (box 706) result in a modification to the balance of fuel input to the gasifier, the stoichiometric oxygen flow rate M_O2,stand hence the gasifier oxygen flow set point M_O2,spare also affected. As such, adjustment of the gasifier oxygen flow M_O2-G(box 708) is initiated.
While the first comparator step 702 monitors and reacts to process furnace variables, the gasifier comparator step 732 performs an analogous function for the gasifier 300. That is, gasifier temperature is measured (box 710) and syngas quality is measured (box 712) and inputted to the gasifier comparator step 732.
Temperature measurement (syngas and/or gasifier internal) permits enhanced process control, operability, and durability. Temperatures below a lower predetermined temperature, which can be defined by the gasifier type and fuel composition, result in insufficient syngas output and quality and gasifier efficiency below a desired level, due principally to slower reaction kinetics. Moreover, in slagging gasifiers, sufficiently high temperature is sustained to maintain slag (molten ash) in a molten flowing condition. Temperatures below a predetermined temperature within the gasifier, which depend substantially on ash composition, will result in local slag solidification, and will eventually deteriorate into a loss of fuel throughput condition and subsequent system shutdown. Excessively high temperature is also deleterious to the gasification process in that it leads to more rapid degradation (corrosion, erosion, and/or thermal stress) of high temperature components such as refractory, heat transfer surfaces, syngas transport pipe, and flow control devices. Further, over-temperature conditions in slagging gasifiers lead to slag viscosities that are too low, causing the slag to drain too rapidly from the gasifier and thereby withdrawing the natural protection that the slag affords the underlying refractory surface, whereas over-temperature conditions in non-slagging gasifiers, such as bed-type gasifiers, can lead to gasifier plugging and subsequent mal-distribution of reactants.
In heating and power applications, measurement of syngas composition can be used to derive the syngas heating value H_sgas well as to predict the stability and temperature of the syngas flame in the process furnace. That is, knowledge of the syngas heating value, in addition to aiding in the quantification of the process furnace energy balance, permits assessment of the quality of energy delivered to the furnace 102. For example, when the syngas is used as a fuel input to a boiler originally designed to fire a conventional fossil fuel such as coal, fuel oil or natural gas, the syngas heating value is greater than or equal to a minimum value H_sg,min, in order to maintain parity with the performance of the furnace using the baseline fuel. The specific furnace performance considerations extend to heat transfer rate and distribution, process temperatures, original flow control and delivery equipment (e.g., pipes, valves, burners), and original emissions control equipment. Syngas hydrogen (H₂) concentration is another component of syngas composition. While hydrogen and carbon monoxide (CO), for example, have similar heating values (molar basis) and burn at similar temperatures, hydrogen is a much more highly reactive gas that diffuses and combusts very rapidly. As such, the concentration of H₂in the syngas will substantially influence the flame stability. Quantification of the effect of H₂concentration on flame stability S_Lcan be seen in its influence on the laminar flame speed, which is a combustion parameter that directly relates to reaction rate and flame stability. The higher the laminar flame speed, the higher the reaction rate and the more robust the flame stability. Prior art measurements of the peak value of S_Lfor combustion of H₂, CO and CH₄in air are summarized in Table 1. Note that the peak value of S_Lfor H₂is roughly an order of magnitude greater than that for either CO or CH₄. Hence, even small concentrations of hydrogen added in a fuel gas mixture can substantially increase flame speed and improve flame stability. For a given solid fuel feed and gasifier design, hydrogen concentration in the products syngas can be increased, for example, by strategic injection of water or steam into the gasifier.

TABLE 1

Data taken from Lewis and Von Elbe, Combustion, Flame and Explosion
of Gases, 3^rdEdition, Academic Press, New York, 1987.

		Peak Laminar Flame Speed
	Fuel	(cm/sec)

	H₂	320
	CH₄	35
	CO	45

Measurement of syngas composition is also used for applications wherein syngas is used in the production of chemicals. In such cases, measurement of syngas composition may be utilized, for example, to maintain a fixed CO/H₂ratio or control CH₄production within specified limits.
While syngas heating value and composition do not possess a unique relationship to one another (i.e., several different gas compositions can and do yield the same gas heating value), repeatable and predictable relationships will occur between the composition and heating value for particular fuels gasified in a fixed gasifier. Therefore, for a given solid fuel/gasifier combination, measurement of gaseous species that will adequately satisfy the calculation of heating value and assessment of syngas quality include, but are not limited to, carbon monoxide (CO), hydrogen (H₂), methane (CH₄) and carbon dioxide (CO₂), alone or in combination.
Returning to the diagrammatic view of the control system 305 in FIG. 3, if the measured gasifier temperature and syngas composition are within a predetermined range, then the control system 305 bypasses the gasifier controls and returns to its gasifier monitoring/comparing function (see return step 734) while, in parallel, also proceeding back to the first comparator step 702 (see return step 728). This parallel functionality enables the multiple gasifier controls to be activated and executed simultaneously. If, however, either of the gasifier variables possess deviations from the predetermined range, the control system 305 initiates a gasifier control step 720. The gasifier control step 720 includes one or more of the following: adjusting the solid fuel flow rate (box 724), adjusting the recycled syngas flow rate (box 714), and adjusting the gasifier oxygen flow rate (box 716). These adjustments are based upon the measured gasifier temperature (box 710) and/or the measured syngas composition and/or heating value (box 712).
Adjusting the recycled syngas flow rate (box 714) controls the supplemental fuel input (for example, fuel provided in addition to solid fuel) to the gasifier 300. As such, it affects gasifier temperature. That is, higher rates of supplemental energy input from the recycled syngas generally lead to higher gasifier temperature. Conversely, lower rates of supplemental energy input from the recycled syngas generally lead to lower gasifier temperature. When, however, the energy density and/or the quality of the recycled syngas is too low, increases in the rate of recycled syngas can lead to a lowering of the gasifier temperature. Analysis of the product gas quality and measurement of the gasifier temperature are used to assess the effect that an incremental decrease or increase of recycled syngas will have on gasifier temperature. One method of quantifying this assessment is through the calculation of adiabatic flame temperature of the recycled syngas. When the recycled syngas flame temperature is higher than the flame temperature of the solid fuel within the gasifier, then incremental addition of recycled syngas will generally increase the gasifier temperature. However, when the flame temperature of the recycled syngas is lower than that of the solid fuel within the gasifier, then incremental addition of recycled syngas will generally lead to a reduction in gasifier temperature. In addition to the preceding considerations, the ratio of recycled syngas to solid fuel input determines the combined input fuel composition, which directly affects syngas quality. Adjusting the gasifier oxygen flow rate (box 716) controls the degree of partial oxidation within the reactor, which affects syngas composition, and also temperature through the chemical energy release of the fuel (i.e., more oxidation leads to higher chemical energy release and higher gasifier temperature, etc.). Adjusting the oxygen flow rate (box 716) is optionally followed in series by adjusting oxygen flow rate with recycled syngas (box 718) which controls the proportion of gasifier oxygen introduced with, or adjacent to, recycled syngas. That is, at fixed total gasifier oxygen flow rate M_O2-G, a portion M_O2-G2of this total can be introduced adjacent to the recycled syngas stream as indicated in FIGS. 1 and 2. The advantages of such a technique relate in part to reducing or eliminating the dilution between this latter oxygen stream and the recycled syngas, which leads to higher recycled syngas flame temperature and, hence, higher rates of heat transfer from the recycled syngas flame to its surroundings within the gasifier. There are other advantages, such as those disclosed in U.S. patent application Ser. No. ______, titled “Method for Gasification and Gasifier,” filed concurrently with the present disclosure and incorporated by reference in its entirety.
The relationship between solid fuel flow rate and gasifier temperature is similar to that between the recycled syngas flow rate and temperature already disclosed. There are, however, differences between the adjusting of the solid fuel flow rate (box 724) and adjusting the recycled syngas flow rate (box 714). First, since the solid fuel energy input to the gasifier controls the energy input to the process furnace (see equation 11), under conditions of constant solid fuel quality, the solid fuel flow rate will not be altered unless the process furnace 102 demand changes (see box 706). This is different from the logic of recycled syngas flow control, which is invoked to modulate gasifier temperature at fixed solid fuel quality and process furnace 102 demand. When however, solid fuel quality varies, then a change in solid fuel flow rate to the gasifier 300 may be required to maintain steady process conditions within the process furnace. That is, higher solid fuel energy density (e.g., HHV) would require a lower solid fuel flow rate and lower solid fuel energy density would require a higher flow rate.
Upon completion of the gasifier control step 720, the control system 305 initiates a return step 726 that initiates measurement of the gasifier temperature (box 710) and/or measurement of the syngas composition and/or heating value (box 712). This loop is repeated until convergence with gasifier 300 set point parameters is attained, and the gasifier comparator step 732 directs the control system 305 to initiate the first comparator step 702. Note that there is a possible scenario in which gasifier convergence cannot be attained due, for example, to low solid fuel quality preventing the attainment of sufficiently high quality syngas to satisfy the process furnace 102 operating requirements. In such circumstances, the control system 305 has the option of introducing oxygen into the process furnace 102 (see M_O2-Fon FIG. 2) in order to enhance the syngas flame characteristics in the furnace. Thus, modulation of oxygen (box 722) is initiated by adjusting control valve 321 to regulate the process furnace 102 oxygen flow in accordance with the process furnace 102 performance parameters.
The control system 305 addresses the drawbacks of the prior art by employing recycle of syngas generated in the gasifier 300 to enable a rapid and dynamic response to changes in process furnace 102 demand while maintaining stable operation of the system 100. In one embodiment, the recycled syngas generates a flame temperature that is higher than the flame temperature of the primary solid fuel within the gasifier 300. This is achieved by elevating flame temperature of the recycled syngas by burning the recycled syngas stream with oxygen. The benefits that can be derived by burning a secondary fuel with oxygen in a solid fuel reactor include, but are not limited to, improved reactor turndown, improved product gas consistency and ability to gasify fuels with a broad range of slagging properties. The increases in the flame temperature afforded by oxygen combustion are illustrated in Table 2, which shows the adiabatic flame temperatures of a typical syngas in both stoichiometric (zero excess oxidizer) air and oxygen combustion. It is instructive to compare these values to the typical adiabatic flame temperature of solid fuel, for example, bituminous coal which has an adiabatic flame temperature of about 3600° F. (4060 R). As radiant heat transfer is proportional to (T_high ⁴−T_low ⁴), where T is the absolute temperature (either Rankine, R or Kelvin, K), it is clear that the heat transfer from an oxy/syngas flame to coal in a gasifier will transfer substantially more heat than would occur from an air/syngas flame.

	TABLE 2

	Constituent	Syngas

Carbon Monoxide	58	mol %
Hydrogen	21	mol %
Methane	8	mol %
Carbon Dioxide	5	mol %
Water Vapor	4	mol %
Nitrogen	4	mol %
Higher Heating Value	337	Btu/scf
Adiabatic Flame	3683°	F. (4143 R)
Temperature in Air
Adiabatic Flame	5087°	F. (5547 R)
Temperature in
Oxygen

In one embodiment, rapid and dynamic response to process furnace 102 energy demand changes is achieved by diverting a variable portion of the syngas product back to the gasifier in a recycle stream. That is, when process energy demand is reduced, syngas product is diverted away from the process to the recycle line. Conversely, when process energy demand is increased, syngas flow to the process is increased by diverting flow from the recycle line back to the process.
In another embodiment, a safe and stable increase in turndown of the gasifier 300 and, consequently, a larger system (gasifier 300 plus dedicated process furnace 102), is achieved by reducing or eliminating gasifier 300 temperature and syngas quality variations during turndown. For example, the control system 305 achieves temperature stabilization during turndown by off-setting the reduction in gasifier temperature that a reduction in solid fuel energy input to the gasifier would otherwise bring, by combining a portion of the recycled syngas with a portion of the oxygen, thereby enhancing heat transfer from the recycled syngas flame via the increase in recycled syngas flame temperature that oxygen affords. The syngas quality stabilization derives both from the temperature stability and the use of feedback from syngas quality and gasifier temperature measurements as input to the control system 305 to adjust oxygen and recycled syngas rates. For example, the gasifier 300 temperature may require additional syngas recycle flow as solid fuel feed is reduced, while syngas stabilizing heating value may be affected by reducing or increasing oxygen introduced to the gasifier 300. Increasing oxygen flow, for example, increases fuel oxidation which may decrease (or prevent an increase) in syngas heating value. Decreasing oxygen flow decreases oxidation which may, for example, increase syngas heating value.
Further details describing aspects of the functionality of the control system 305 are presented in the following, non-limiting examples.

EXAMPLE

The Examples described herein are intended to further describe the functionality of the control system 305 and to illustrate prophetic aspects of the application of the control system 305. Although assumptions are made for the purposes of simplicity and clarity, those skilled in the art will appreciate that the assumptions can (and often will) be removed and replaced with more specific and more precise calculations and modeling based upon the operational considerations of the system controlled by the control system 305.
Each of the Examples relates to a gasifier burning agricultural waste with oxygen to produce syngas that is delivered to a boiler where it is combusted with air to raise steam and generate electricity. Chemical properties of the agricultural waste (solid fuel) are listed in Table 3.

TABLE 3

Solid Fuel Properties

	Agricultural Waste
	Constituent	Concentration (wt %)

	Carbon	40.90
	Hydrogen	5.15
	Oxygen	36.62
	Nitrogen	0.92
	Water	11.27
	Ash	5.15
	Higher Heating Value	6959
	(Btu/lb, as recv'd)

The baseline fuel energy delivered to the boiler in the syngas is equal to 200 MMBtu/hr, with reference to the higher heating value of the syngas. The overall efficiency of the gasifier is 85%. That is, 15% of the energy entering the gasifier is lost and not thereafter recovered. Ten percent of the syngas generated in the gasifier is recycled back to the gasifier input for supplemental heat. Oxygen is introduced into the gasifier at 25% of the stoichiometric amount. The syngas Higher Heating Value (HHV) is maintained above 300 Btu/scf for boiler combustion stability, and the gasifier internal temperature is greater than 2000° F. to ensure slagging conditions, but less than 2200° F. to prevent excessive corrosion and refractory degradation within the gasifier. It is assumed that the recycled syngas flame temperature is greater than the solid fuel flame temperature within the gasifier. The baseline syngas composition is given in Table 4.

TABLE 4

Baseline Syngas Properties

		Concentration
	Syngas Component	(mol %)

	CO	55
	H2	25
	CH4	5
	CO2	5
	N2	5
	H2O	5
	Higher Heating Value	310.5 Btu/scf

Energy flows around the system for baseline and subsequent the first adjustment step 730 are summarized in Table 5. Mass flows of solid fuel and oxygen to the gasifier for the same conditions are listed in Table 6. Details regarding the exemplary baseline calculations and first adjustment step 730 actions are subsequently provided herein.

TABLE 5

Energy Flows (MMBtu/hr) Following
Primary Control Block Actions

	Control Step	Control Step
	704: Adjust	706: Adjust	Control Step
	Recycle	Solid Fuel	708: Adjust
Baseline	Syngas Flow	Flow	O2 Flow

Boiler In	200	190	190	190
Gasifier	222.2	232.2	222.2	222.2
Out
Syngas	22.2	42.2	32.2	32.2
Recycle
Solid Fuel	239.2	239.2	229.2	229.2
to
Gasifier
Gasifier	39.2	39.2	39.2	39.2
Energy
Loss

Syngas Recycle Ratio, β

	0.10	0.182	0.145	0.145

TABLE 6

Mass Flows (lb/hr) of Solid Fuel and Oxygen to Gasifier
Following Primary Control Block Actions

Solid	34,375	34,375	32,938	32,938
Fuel
Oxygen	10,510	10,510	10,510	10,438

Stoichiometric Ratio, φ

	0.250	0.235	0.252	0.250

After a period of steady operation at these baseline conditions, the boiler energy demand is reduced to 190 MMBtu/hr. To rapidly facilitate the reduction in demand, the adjustments to syngas flow rate (box 704) by the control system 305 reduce the flow of syngas to the boiler by adjusting the position of syngas control valve 307. The speed of recycled syngas blower 315 and/or the position of the recycled syngas control valve 319 can also be adjusted to redirect that portion of the boiler syngas that has been reduced back to the gasifier through the recycle line. This initial control response occurs without altering either the gasifier oxygen or solid fuel flows. Moreover, since it occurs rapidly, overall energy loss from the gasifier 300 is maintained at the baseline level. It is assumed for the purpose of this example that the syngas composition remains constant during the first adjustment step 730. Variations to syngas quality are addressed subsequently during the gasifier control step 720.
Note that after the initial adjustments to syngas flow rate (box 704), the recycle ratio, β (included in Table 5), increases from 0.10 to 0.182, while the oxygen stoichiometric ratio, φ (included in Table 6), drops from 0.250 to 0.235 due to the higher syngas recycle flow to the gasifier at fixed oxygen flow rate. When the solid fuel flow is reduced to the new boiler demand by adjustments to solid fuel flow rate (box 706), the syngas recycle flow is also lowered from the rapid response adjustments to syngas flow rate (box 704) to a value that returns the total (recycled syngas plus solid fuel) gasifier energy input to the baseline value. While this particular reduction is only one of many specific allowable control actions controlled by the control system 305, it is beneficial in that it provides gasifier energy input and, hence, temperature stability during boiler load fluctuations. While the oxygen flow to the gasifier remains constant during adjustments to solid fuel flow rate (box 706), it is of interest that the stoichiometric ratio φ increases due to the reduction in fuel flow. Ultimately, the gasifier oxygen flow is adjusted (box 708). It is noteworthy that, while the stoichiometric ratio set point is equal to its baseline value of 0.25, the corresponding oxygen flow rate is somewhat reduced from its baseline level due to the higher proportion of syngas to solid fuel entering the gasifier (syngas requiring slightly less oxygen per Btu than the solid fuel). Retaining a constant stoichiometric ratio is, as with total gasifier energy input, one of many specific control formulae that can be applied. In this case, the rationale is that maintaining a constant stoichiometric ratio will, at first approximation, provide a reduced or eliminated disruption to syngas quality during the control adjustment process.
If the first adjustment step 730 maintains stability of gasifier temperature and syngas quality during the period of transitional boiler demand, then the measurement of the gasifier temperature (box 710) and/or measurement of the syngas composition and/or heating value (box 712) will confirm that no further control action is required. Nevertheless, for the purpose of documenting in a logical manner the method of operation of the control system 305, four prophetic Examples involving disruptions to steady gasifier operation were considered by applying the above parameters and assumptions.

Example 1

Low Syngas Heating Value

In a first Example, measurement of the syngas composition reveals that the CO concentration decreases by 5 mol % while the CO₂concentration increases by the same percentage as a result of the first adjustment step 730, lowering the syngas HHV to 294.5 Btu/scf (see Table 7 for a breakdown of the system 100 parameters, including syngas properties, energy and mass flows before and after the gasifier control step 720 actions).

TABLE 7

Key System Parameters for Example 1: Low Syngas HHV

	State 1a: Following First
	Adjustment Step
730

	but Prior to Gasifier	State 1b: Following
Syngas Component	Control Step	720	Gasifier Control Step 720

CO	50	mol %	55	mol %
H₂	25	mol %	20	mol %
CH₄	5	mol %	10	mol %
CO₂	10	mol %	5	mol %
N₂	5	mol %	5	mol %
H₂O	5	mol %	5	mol %
Syngas HHV	294.5	Btu/scf	344.8	Btu/scf
Gasifier	2080°	F.	2050°	F.
Temperature
Energy to Boiler	190	MMBtu/hr	190	MMBtu/hr
Energy out of	222.2	MMBtu/hr	222.2	MMBtu/hr
Gasifier
Syngas Recycle	32.2	MMBtu/hr	32.2	MMBtu/hr
Energy
Solid Fuel Energy	229.2	MMBtu/hr	229.2	MMBtu/hr
Gasifier Energy	39.2	MMBtu/hr	39.2	MMBtu/hr
Loss

Syngas Recycle

0.145

Ratio, β
Solid Fuel Flow	32938	lb/hr	32938	lb/hr
Rate
Oxygen Flow Rate	10441	lb/hr	9639	lb/hr

Stoichiometric	0.250	0.230
Ratio, φ

Since the gasifier temperature is within the predetermined range, the oxygen flow rate is reduced in order to prevent the amount of fuel oxidation taking place from exceeding a predetermined degree. As such, the oxygen flow rate is adjusted (box 716) and the oxygen flow is incrementally reduced until the syngas heating value is raised once again above 300 Btu/scf. The final value for the stoichiometric ratio is 0.230. The gasifier temperature remains within acceptable limits, dropping from 2080° F. to 2050° F. due to the lower degree of partial oxidation, and hence chemical energy release, within the gasifier 300.

Example 2

Low Gasifier Temperature

In a second Example, the syngas heating value remains within the predetermined range, but the gasifier temperature is lowered to 1980° F., which is lower than a desired range based on slagging considerations. This can happen for several reasons, such as lower feedstock quality or higher gasifier dilution resulting from the higher ratio of syngas to solid feedstock energy input relative to baseline conditions. The oxygen flow rate is adjusted (box 716) to increase the gasifier oxygen flow rate, thereby oxidizing more of the fuel inside the gasifier and releasing more thermal energy. The stoichiometric ratio φ thus incrementally increases until the gasifier temperature rises back above 2000° F. A value of φ equal to 0.27 results in a gasifier temperature of 2020° F. while maintaining the syngas HHV above 300 Btu/scf. System 100 parameters of the gasifier 300 for the second Example are provided in Table 8.

TABLE 8

Key System Parameters for Example 2: Low Gasifier Temperature

	State 2a: Following First
	Adjustment Step
730

	but Prior to Gasifier	State 2b: Following
Syngas Component	Control Step	720	Gasifier Control Step 720

CO	55	mol %	53	mol %
H₂	25	mol %	25	mol %
CH₄	5	mol %	5	mol %
CO₂	5	mol %	7	mol %
N₂	5	mol %	5	mol %
H₂O	5	mol %	5	mol %
Syngas HHV	310.5	Btu/scf	304.1	Btu/scf
Gasifier	1980°	F.	2020°	F.
Temperature
Energy to Boiler	190	MMBtu/hr	190	MMBtu/hr
Energy out of	222.2	MMBtu/hr	222.2	MMBtu/hr
Gasifier
Syngas Recycle	32.2	MMBtu/hr	32.2	MMBtu/hr
Energy
Solid Fuel Energy	229.2	MMBtu/hr	229.2	MMBtu/hr
Gasifier Energy	39.2	MMBtu/hr	39.2	MMBtu/hr
Loss

Syngas Recycle	0.145	0.145
Ratio, β

Solid Fuel Flow	32938	lb/hr	32938	lb/hr
Rate
Oxygen Flow Rate	10438	lb/hr	11275	lb/hr

Stoichiometric	0.250	0.270
Ratio, φ

Example 3

High Gasifier Temperature

In a third Example, high gasifier temperature results from first adjustment step 730 actions. Measurement of the gasifier temperature (box 710) detects the high temperature condition. The control system 305 responds by reducing the syngas recycle flow rate (box 714), since this lowers the total energy input to the gasifier 300 without affecting the energy delivered to the boiler. System 100 parameters corresponding to the initial and final condition for this case are summarized in Table 9.

TABLE 9

Key System Parameters for Example 3: High Gasifier Temperature

	State 3a: Following First
	Adjustment Step
730

Syngas	but Prior to Gasifier	State 3b: Following
Component	Control Step	720	Gasifier Control Step 720

CO	55	mol %	55	mol %
H₂	25	mol %	25	mol %
CH₄	5	mol %	5	mol %
CO₂	5	mol %	5	mol %
N₂	5	mol %	5	mol %
H₂O	5	mol %	5	mol %
Syngas HHV	310.5	Btu/scf	310.5	Btu/scf
Gasifier	2230°	F.	2180°	F.
Temperature
Energy to Boiler	190	MMBtu/hr	190	MMBtu/hr
Energy out of	222.2	MMBtu/hr	215.9	MMBtu/hr
Gasifier
Syngas Recycle	32.2	MMBtu/hr	25.9	MMBtu/hr
Energy
Solid Fuel Energy	229.2	MMBtu/hr	228.1	MMBtu/hr
Gasifier Energy	39.2	MMBtu/hr	38.1	MMBtu/hr
Loss

Syngas Recycle	0.145	0.12
Ratio, β

Solid Fuel Flow	32938	lb/hr	32778	lb/hr
Rate
Oxygen Flow Rate	10438	lb/hr	10180	lb/hr

Stoichiometric	0.250	0.250
Ratio, φ

The solid fuel flow rate to the gasifier drops slightly since the energy loss, as a fraction of the total gasifier energy input, remained constant while the total energy input was lowered due to the reduced syngas recycle flow. Moreover, the oxygen flow rate to the gasifier significantly reduces since the stoichiometric ratio remains constant while the gasifier fuel input (solid plus recycled syngas) is lowered.

Example 4

High Syngas Heating Value Due to Variation in Solid Fuel Feedstock Properties

A fourth Example shows that although an increase in syngas heating value is not detrimental to the operation of either the gasifier 300 or boiler, without control system 305 intervention is nevertheless still desired to maintain substantially constant energy flow to the furnace. For example, an increase of syngas HHV from 310.5 to 376.0 Btu/scf occurring as a result of an increase in the quality of solid fuel feedstock from the original fuel described in Table 3 to a higher carbon, lower moisture fuel was analyzed. The upgraded solid fuel composition is provided in Table 10. System 100 parameters following the initial boiler load reduction (original solid fuel), and following the solid fuel/syngas HHV variation, respectively, are summarized in Table 11.
In this example, as the energy density of the syngas increases, the rate of energy supplied to the furnace 102, at fixed fuel mass flow rates would increase proportionally. To maintain substantially constant energy flow to the furnace 102, the control system 305 responds to an increase in syngas HHV by executing a reduction in syngas mass flow rate (box 704) through control valve 307. If it is assumed that the control system 305 has also received data indicating an increase in the HHV of the solid fuel, then there would also be a (feed-forward) reduction in solid fuel flow rate (see box 706) to a value that would maintain a substantially constant solid fuel energy input rate to the gasifier 300. This would then be followed by an adjustment (box 708) to oxygen flow to account for the different balance of solid fuel and recycled syngas to the gasifier 300. In one embodiment, all of these primary control block actions can be executed without actions of gasifier control step 720.

TABLE 10

Adjusted Solid Fuel Properties

	Solid Fuel
	Constituent	Concentration (wt %)

	Carbon	53.1
	Hydrogen	6.6
	Oxygen	30.5
	Nitrogen	0.8
	Water	2.0
	Ash	7
	Higher Heating Value	8050
	(Btu/lb, as recv'd)

TABLE 11

Key System Parameters for Supplemental Case: High Syngas HHV

	State 4a: Following	State 4b: Following State
	Energy Demand reduction	4a and after Additional
	and After First	Control Adjustments
	Adjustment Step
730	Resulting from Shift in
Syngas	with Solid Fuel as	Solid Fuel Properties
Component	in Table 3	from Table 3 to Table 10

CO	55	mol %	55	mol %
H₂	25	mol %	24	mol %
CH₄	5	mol %	12	mol %
CO₂	5	mol %	5	mol %
N₂	5	mol %	1	mol %
H₂O	5	mol %	3	mol %
Syngas HHV	310.5	Btu/scf	376	Btu/scf
Gasifier	2080°	F.	2080°	F.
Temperature
Energy to Boiler	190	MMBtu/hr	190	MMBtu/hr
Energy out of	222.2	MMBtu/hr	222.2	MMBtu/hr
Gasifier
Syngas Recycle	32.2	MMBtu/hr	32.2	MMBtu/hr
Energy
Solid Fuel Energy	229.2	MMBtu/hr	229.2	MMBtu/hr
Gasifier Energy	39.2	MMBtu/hr	39.2	MMBtu/hr
Loss

Syngas Recycle	0.145	0.145
Ratio, β
Relative Syngas	1.0	0.826
Molar Flow Rate
to Boiler

Solid Fuel Flow	32938	lb/hr	28474	lb/hr
Rate
Oxygen Flow	10438	lb/hr	12799	lb/hr
Rate

Stoichiometric	0.250	0.250
Ratio, φ

Reference to Table 11 shows that while the energy flow rate to the furnace 102 remains unaltered as a result of the high syngas HHV condition, the molar (i.e., volumetric) flow of syngas to the boiler decreases by 17.4% from the post-boiler load reduction/original solid fuel value, changing from a relative value of 1.0 to 0.826 (see “Relative Syngas Molar Flow Rate to Boiler” entry in Table 11). In addition, the solid fuel flow rate lowers due to the increase in solid fuel HHV and the oxygen flow rate increases significantly, even though the stoichiometric ratio remains at 0.25. This is because the stoichiometric molar ratio of oxygen added to carbon in the solid fuel to ω_stoichincreases due to the change in both solid fuel and recycled syngas composition.
It has been assumed in the preceding Example that the change in solid fuel composition was detected in a timely manner and inputted into the control system 305. However, the control system 305 can function effectively in the absence of this measurement. This is because, in such a case, the deviation in syngas quality will still be detected in the furnace 102 as an increase in energy input. Hence, the syngas flow rate to the furnace 102 will still be gradually reduced via adjustment to syngas flow rate (box 704). However, at this stage, since no solid fuel flow rate data are available, the control system will not execute an adjustment in solid fuel flow rate (see box 706). Instead, after executing necessary adjustments to the oxygen flow rate due to any change in recycled syngas flow that may accompany the change in positioning of control valve 307, the control system 305 proceeds to gasifier measurements (see box 710 and box 712), and the gasifier comparator step 732. Due to the increase in solid fuel HHV and constant feed rate, the gasifier 300 temperature will rise, thereby directing the control system to enter the gasifier control step 720 where the three pathways of solid fuel, recycled syngas, and oxygen adjustment are available, alone or in tandem. The simultaneous existence of high gasifier temperature and high syngas HHV will instruct the control system 305 to lower the gasifier energy input via either the solid fuel (box 724) or recycled syngas (box 714) flow reduction mechanisms. However, as a unilateral reduction in recycle flow (box 714) would, all other factors remaining constant, increase the syngas delivered to furnace 102 (i.e., displaced recycled syngas will go to furnace), which in this case is not desired, this would not be a suitable response. The appropriate response to this scenario is thus a reduction in solid fuel flow rate (box 724), just as it was when solid fuel quality data were available. Hence, the control system 305 executes this response while continuing to monitor the furnace 102 and gasifier 300 performance parameters for compliance, and invoking refining adjustments along the path to stable and efficient operation of the system 100.
While the preceding example provides specific options and methods of control of the control system, it will be clear to one skilled in the art that numerous other scenarios and responses not covered herein are possible. The particular control actions delimited in this inventive disclosure are, therefore, to be adaptive to the particulars (i.e., gasifier design, furnace design, fuel properties, etc.) of the system it serves. Furthermore, while the invention has been described with reference to one or more preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A method of controlled gasification, the method comprising:

introducing a first fuel to a gasifier in a system;

generating a product gas by partially oxidizing the first fuel with an oxidizer including oxygen;

directing a first portion of the product gas to a process chamber; and

selectively introducing a recycled portion of the product gas to the gasifier;

wherein a quality parameter of the product gas is analyzed;

wherein introduction of the oxidizer and the selective introduction of the recycled portion of the product gas is based upon the quality parameter of the product gas stream; and

wherein the first fuel includes a solid fuel.

2. The method of claim 1, wherein the first portion of the product gas directed to the process chamber is directed based upon an energy value signal from the process chamber.

3. The method of claim 1, further comprising selectively introducing a second fuel with the first fuel, the second fuel having a different phase and composition than the first fuel.

4. The method of claim 1, wherein the process chamber is a furnace.

5. The method of claim 1, wherein the process chamber is a gas turbine.

6. The method of claim 3, wherein the energy value signal corresponds to an amount of output from a generator powered by the system.

7. The method of claim 3, wherein the energy value signal corresponds to one or more of a temperature, a pressure, and a flow rate of a stream within the system, or the energy value signal corresponds to a representative temperature of a component within the system.

8. The method of claim 1, further comprising selectively introducing one or more additives to the gasifier, the one or more additives being selected from the group consisting of fly ash, compounds containing calcium, compounds containing magnesium, compounds containing silicon, compounds containing aluminum, compounds containing iron, and any combination thereof.

9. The method of claim 1, further comprising selectively introducing water or steam to the gasifier.

10. The method of claim 1, further comprising selectively introducing oxygen to the gasifier proximal to the recycled portion of the product gas.

11. The method of claim 1, further comprising selectively introducing oxygen to the process chamber.

12. The method of claim 1, wherein the analysis of the product gas stream includes identifying a concentration of CO in the product gas stream.

13. The method of claim 1, wherein the analysis of the product gas stream includes identifying a concentration of H2 in the product gas stream.

14. A system for performing the process of claim 1.

15. A system for controlled gasification, the system comprising:

a gasifier configured to receive a first fuel and generate a product gas by partially oxidizing the first fuel with an oxidizer including oxygen;

an analyzer configured to analyze a quality parameter of the product gas; and

a controller configured to receive a product gas quality signal and to respond to the product gas quality signal by initiating selective adjustment of one or more of an oxygen flow rate being introduced to the gasifier, a recycled product gas flow rate being introduced to the gasifier, and a flow rate of the first fuel;

wherein the system is configured to recycle at least a portion of the product gas to the gasifier;

wherein the first fuel includes solid fuel.

16. The system of claim 15, wherein the controller is further configured to receive an energy value signal and to initiate an adjustment in a flow rate of the product gas to a process chamber in response to the energy value signal.

17. The system of claim 15, wherein the product gas quality signal includes a concentration of one or more of CO, H2, CH4, and CO2 in the product gas and a representative temperature of the gasifier.

18. A system for controlled gasification, the system comprising:

a gasifier configured to receive a first fuel and generate a product gas by partially oxidizing the first fuel with an oxidizer including oxygen; and

a controller configured to receive an energy value signal and to initiate an adjustment in a flow rate of the product gas to a process chamber in response to the energy value signal;

wherein the first fuel includes solid fuel.

19. The system of claim 18, wherein the controller is further configured to receive a product gas quality signal and to respond to the product gas quality signal by initiating selective adjustment of one or more of an oxygen flow rate being introduced to the gasifier, a recycled product gas flow rate being introduced to the gasifier, and a flow rate of the first fuel.

20. The system of claim 19, wherein the process chamber is configured to receive selectively introduced oxygen.