CN104793050A - Method for calculating denitration on-grid electric quantity of thermal power plant - Google Patents

Abstract

The invention discloses a method for calculating denitration on-grid electric quantity of a thermal power plant. The method includes: calculating quantity of NOx removed by a denitration device in an operation process of the thermal power plant, calculating a theoretical minimal denitration agent input quantity, judging whether denitration is effective or not according to the calculated quantity and acquired real-time data, and calculating noneffective denitration electric quantity to further calculate denitration on-grid electric quantity. By adoption of the method for calculating the denitration on-grid electric quantity of the thermal power plant, a closed-loop feedback information passage for operation management of a denitration system can be established between a grid company and the thermal power plant possibly. Electricity purchasing and selling contract management and denitration management of grid-connected thermal power plants can be standardized beneficially to provide pollutant emission statistical data and regulatory basis for functional government departments so as to benefit improvement of air quality and protection of ecological environment. In addition, promotion of standardization, marketization and legalization of denitration operations is supported technically.

Description

The computing method of thermal power plant's denitration electricity volume

Technical field:

The present invention relates to automated control technology, particularly the computing method of a kind of thermal power plant denitration electricity volume.

Background technology:

Electrical production in 2014, increases by 3.6% than last year.Classifying type is seen, water power generated energy 10,661 hundred million kilowatt hour, increases by 19.7% on a year-on-year basis, account for 19.2% of national generating capacity, improve 2.6 percentage points than last year; 3.3 percentage points are reduced than last year; Nuclear power, grid connected wind power and grid-connected solar electrical energy generation amount are respectively 1,262 hundred million kilowatt hours, 1,563 hundred million kilowatt hours and 23,100,000,000 kilowatt hours, increase by 13.2%, 12.2% and 171% respectively on year-on-year basis, the proportion accounting for national generating capacity improves 0.2,0.2 and 0.3 percentage point respectively than last year.According to the statistics in national environmental protection portion, 2013, national nitrogen oxide emission 2227.4 ten thousand tons, investigation Thermal Power Generation Industry 3102, NOx discharge 964.6 ten thousand t, accounted for 43.3% of national NOx discharge, accounts for 62.4% of industrial NOx discharge.Visible Thermal Power Generation Industry is still the maximum industry of NOx discharge.Therefore the pollution controlling the NOx of thermal power plant's industry is imperative.

The emission control requirement to SO2, NOx, dust and mercury is proposed according to the GB13223-2011 " fossil-fuel power plant atmospheric pollutant emission standard " playing enforcement on January 1st, 2012, from 1 day January in 2012, newly-built thermal power generation boiler and gas turbine group held new emission limit; From 1 day July in 2014, existing thermal power generation boiler and gas turbine group performed new emission limit.The special emission limit of atmosphere pollution that the thermal power generation boiler of key area and gas turbine group perform.Perform the concrete territorial scope of the special emission limit of atmosphere pollution, implement the time, specified by competent administrative department for environmental protection of State Council.Current NOx emission controls to be the important content that atmosphere pollution is administered.

At present, the controlling soil moist of the NOx of domestic and international application has three kinds: LNB (low NOx Burner low NO), SNCR (Selective Non-Catalytic Reduction SNCR), and SCR (Selective Catalytic Reduction) is SCR technology.Wherein, SCR is the denitration mode that current domestic thermal power plant the most extensively adopts, and is the technical way that control NOx pollutes.

In China, " in the face of the resource environment constraint increasingly strengthened, establish green, low carbon development theory; attach most importance to energy-saving and emission-reduction; perfect exciting and restraining system, accelerate to build resources conservation, the eco-friendly mode of production and consumption mode, strengthen the capability of sustainable development." be the strategic objective of national Eleventh Five-Year Plan.According to relevant national standard, the discharge amount of pollution reducing fuel-burning power plant is the important channel of implementing energy-saving and emission-reduction policy.The newly-built denitrating system in fuel-burning power plant, can improve power plant pollution discharge capacity greatly, is the Main Means that current thermal power plant realizes environmental protection operation.

Along with thermal power plant's denitrating system construction and put into operation, shown the problem that some are new especially.First be the enthusiasm that thermal power plant self shortage denitrating system puts into effect.Secondly grid company lacks the technological means of denitrating system operation monitoring, assessment, can not form close-loop feedback thus promote effective control that thermal power plant's denitrating system runs.The accounting of denitration period electricity volume can not be carried out between last grid company and thermal power plant, thus greatly hinder the Market Operation of denitrating system.

Summary of the invention:

The object of the invention is to the defect for existing in above-mentioned prior art, provide a kind of can advance denitration work standardization, the marketization, legalization the computing method of thermal power plant's denitration electricity volume.

For achieving the above object, the present invention adopts following technical scheme to be achieved:

The computing method of thermal power plant's denitration electricity volume, comprise the following steps:

1) calculate the denitrification apparatus NOx amount of removing: the NOx concentration before utilizing flue gas discharge continuous monitoring system Real-time Collection thermal power plant denitrification apparatus and after denitrification apparatus and flue gas flow data, calculate the NOx amount of removing as follows:

The NOx amount of removing (kg/h)=0.001 × ((SCR import NOx mean concentration (mg/Nm ³)-SCR outlet NOx mean concentration (mg/Nm ³)) × exhaust gas volumn (kNm ³/ h);

2) the theoretical minimum input amount of denitrfying agent is calculated: utilize the flue gas flow in thermal power plant's dcs and flue gas discharge continuous monitoring system collection unit running process, generate the NOx concentration of flue gas, the NOx simultaneously specified according to GB13223-2011 allows discharge value, calculates the theoretical minimum input amount of denitrfying agent;

3) determine whether effective denitration according to the real time data of calculated amount and collection, the index of effective denitration is:

A) the NOx amount of removing of denitrification apparatus is less than denitrification apparatus design capacity;

B) utilize thermal power plant dcs to gather desulfurizing agent flow in unit running process, and meet denitrfying agent flow and be greater than the theoretical minimum input amount of denitrfying agent;

C) denitration outlet NOx concentration is less than GB13223-2011 requirement;

D) utilize thermal power plant's dcs to gather denitrification apparatus damper status in unit running process, and meet SCR reactor outlet, inlet baffle standard-sized sheet;

If thermal power unit operation meets above-mentioned requirements in timing statistics section simultaneously, then the discharge of fired power generating unit flue gas NOx is qualified, and denitration electricity counts effective denitration electricity;

If thermal power unit operation does not meet above-mentioned any one requirement in timing statistics section, then the discharge of fired power generating unit flue gas NOx is defective, and denitration electricity counts invalid denitration electricity;

4) calculate invalid denitration electricity, the electricity volume being in the unit of invalid denitration state is defined as invalid denitration electricity; Calculating fee of electric energy system gathers electric quantity data with every N minute interval, dcs with level second interval harvester group active power, simultaneously according to step 4) judge denitration state, and then calculate invalid denitration electricity, wherein, N is not more than 60 minutes;

5) denitration electricity volume is calculated, denitration electricity volume=total electricity-invalid denitration electricity.

The present invention further improves and is: described step 2) calculate the theoretical minimum input amount of denitrfying agent and adopt and obtain with the following method:

The theoretical minimum input amount of denitrfying agent ammonia flow is determined by following formula:

$Q_{\min }=V_m\×F_{\mathrm{ch}}\×\frac{{\mathrm{NOx}}_{\mathrm{in}}-{\mathrm{NOx}}_{\max }}{M_{\mathrm{NO}2}}\×{\mathrm{\ξ}}_1\×{\mathrm{\ξ}}_2\×{\mathrm{\ξ}}_3\×{10}^{-3}---\left(1\right)$

In formula: Q _min---denitrfying agent flow theory minimum value under standard state, m ³/ h;

V _m---the molar volume of gas under standard state, value equals 22.4, L/mol;

NOx _in---with NO ₂meter, at butt mark state and 6%O ₂under state, unit SCR import NOx emission concentration, mg/m ³;

F _ch---at butt mark state and 6%O ₂under state, the total flue gas flow of unit chimney entrance, km ³/ h;

M _nO2---NO ₂molal weight, g/mol;

NOx _max---the NOx emission concentration that GB13223 allows, mg/m ³;

ξ ₁---denitrfying agent flow measurement Ratio for error modification;

ξ ₂---flue gas flow measuring error correction factor;

ξ ₃---nitrous oxides concentration measuring error update the system.

The present invention further improves and is: described step 4) in calculate invalid denitration electricity be adopt to obtain with the following method:

Calculating fee of electric energy system gathers electric quantity data with every N minute interval, adopts the invalid denitration electricity D in the every N of following formulae discovery minute:

$D=\frac{\underset{\mathrm{ti}}{\mathrm{\Σ}}{\∫}_0^{\mathrm{ti}}{P1}_t\mathrm{dt}}{{\∫}_0^N{P}_t\mathrm{dt}}\×E_N---\left(2\right)$

Wherein:

P1 _t---the unit obtained by data processing is in instantaneous power during invalid denitration state;

P _t---from the unit instantaneous power that denitration RTU collects;

T _i---unit is in the duration of invalid denitration state;

E _n---from the every N of the unit minute electricity that calculating fee of electric energy system obtains.

Relative to prior art, utilize the computing method of thermal power plant provided by the invention denitration electricity volume, for the closed loop feedback information passage setting up a denitrating system operational management between grid company and thermal power plant provides possibility.Be conducive to the denitration management of the grid-connected thermal power plant of specification and purchase sale of electricity contract management, for functional government departments provide pollutant emission statistics and supervision foundation, to improving air quality, preserving the ecological environment and will play a positive role.Grid company, thermal power plant can Real-time Obtaining denitrating system operating condition, validity and electricity adjust, and utilize the present invention to be first the enthusiasm that thermal power plant self improves denitrating system and puts into effect; Secondly grid company solves the technical matters of denitrating system operation monitoring, assessment, to form close-loop feedback thus to promote effective control that thermal power plant's denitrating system runs; The accounting of denitration period electricity volume can be carried out between last grid company and thermal power plant, thus greatly facilitate the Market Operation of denitrating system; Simultaneously also to advancing the standardization of denitration work, the marketization, legalization to provide technical support.

For the genset of pilot power plant 2,*60 ten thousand kilowatts, calculate according to every day effective denitration time 95.0%, average load rate 85.0%, produce oxides of nitrogen 43.4 kilograms, after denitration, the discharge capacity of oxides of nitrogen is 6.4 kilograms, can decrease the nitrogen oxide emission of 37.0 kilograms.And putting into operation of denitration information monitoring system will impel each grid-connected thermal power plant to drop into denitrating system according to national regulation, guarantee that the discharged nitrous oxides concentration of separate unit coal unit meets national environmental standard.

Accompanying drawing illustrates:

Fig. 1 is thermal power plant's denitration operation of arriving involved in the present invention and point layout schematic diagram;

Fig. 2 is the process flow diagram of thermal power plant of the present invention denitration electricity volume computing method.

Embodiment:

Illustrate below in conjunction with accompanying drawing and be described in further detail embodiments of the invention, but the present embodiment is not limited to the present invention, every employing similarity method of the present invention and similar change thereof, all should list protection scope of the present invention in.

As shown in Figure 2, the computing method of a kind of thermal power plant denitration electricity volume that the embodiment of the present invention provides, namely utilize the denitration operating condition data of DCS and CEMS system acquisition to calculate the method for the effective denitration electricity volume of thermal power plant, the implementation procedure of the method is as follows:

1) calculate denitrification apparatus NO_x removal amount: the NOx concentration before utilizing flue gas discharge continuous monitoring system Real-time Collection thermal power plant denitrification apparatus and after denitrification apparatus, flue gas flow data, calculate the NOx amount of removing as follows:

The NOx amount of removing (kg/h)=((SCR import NOx mean concentration (mg/Nm ³)-SCR outlet NOx mean concentration (mg/Nm ³)) × exhaust gas volumn (kNm ³/ h), NOx concentration and exhaust gas volumn are obtained by DCS and CEMS system acquisition;

2) denitrfying agent flow is greater than theoretical minimum value, and denitrfying agent ammonia (conversion of all the other type denitrfying agents judges to ammonia) flow theory minimum value is determined by following formula:

$Q_{\min }=V_m\×F_{\mathrm{ch}}\×\frac{{\mathrm{NOx}}_{\mathrm{in}}-{\mathrm{NOx}}_{\max }}{M_{\mathrm{NO}2}}\×{\mathrm{\ξ}}_1\×{\mathrm{\ξ}}_2\×{\mathrm{\ξ}}_3\×{10}^{-3}---\left(1\right)$

In formula: Q _min---denitrfying agent (ammonia) flow theory minimum value (mark state), m ³/ h;

V _m---the molar volume of gas under standard state, value equals 22.4, L/mol;

NOx _in---unit SCR import NOx emission concentration (butt mark state, 6%O ₂under state, with NO ₂meter), mg/m ³;

F _ch---the total flue gas flow of unit chimney entrance (butt mark state, 6%O ₂under state), km ³/ h;

M _nO2---NO ₂molal weight, g/mol;

NOx _max---the NOx emission concentration that GB13223-2011 requires, mg/m ³;

ξ ₁---denitrfying agent flow measurement Ratio for error modification, choose according to each power plant denitrfying agent flow measurement device Surveying Actual Precision;

ξ ₂---flue gas flow measuring error correction factor, choose according to each power-plant flue gas flow measurement device Surveying Actual Precision;

ξ ₃---nitrous oxides concentration measuring error update the system, choose according to each power plant nitrous oxides concentration measurement mechanism Surveying Actual Precision.

3) determine whether effective denitration according to calculated amount, the index of effective denitration is:

A) the NOx amount of removing of denitrification apparatus is less than denitrification apparatus design capacity;

B) denitrfying agent flow is greater than theoretical denitrfying agent flow;

C) denitration outlet NOx concentration is less than GB13223 requirement;

D) SCR reactor outlet, inlet baffle standard-sized sheet (this does not require for none-disk terminal unit);

If thermal power unit operation meets above-mentioned requirements in timing statistics section simultaneously, then the discharge of fired power generating unit flue gas NOx is qualified, and denitration electricity counts effective denitration electricity;

If thermal power unit operation does not meet above-mentioned any one requirement in timing statistics section, then the discharge of fired power generating unit flue gas NOx is defective, and denitration electricity counts invalid denitration electricity.

4) calculate invalid denitration electricity, the electricity volume being in the unit of invalid denitration state is defined as invalid denitration electricity; Calculating fee of electric energy system gathers electric quantity data with every N minute interval, and adopt the invalid denitration electricity D in the every N of following formulae discovery minute, wherein, N is not more than 60 minutes:

$D=\frac{\underset{\mathrm{ti}}{\mathrm{\Σ}}{\∫}_0^{\mathrm{ti}}{P1}_t\mathrm{dt}}{{\∫}_0^N{P}_t\mathrm{dt}}\×E_N---\left(2\right)$

Wherein:

P1 _t---the unit obtained by data processing is in instantaneous power during invalid denitration state;

P _t---from the unit instantaneous power that denitration RTU (remote-terminal unit, Remote Terminal Unit) collects;

T _i---unit is in the duration of invalid denitration state;

E _n---from the every N of the unit minute electricity that calculating fee of electric energy system obtains;

During real system realizes, thermal power plant is gained merit DCS (Distributed Control System (DCS), Distributed Control System) and CEMS (flue gas automatic monitored control system, Continuous Emission Monitoring System) image data carry out Integral Processing and obtain every N minute electricity; By formula manipulation obtain under effective denitration state instantaneous power, and Integral Processing is carried out to this performance number obtain every N minute invalid denitration electricity, then obtain power plant N minute total electricity from calculating fee of electric energy system, obtain invalid denitration electricity by above-mentioned formula.The concrete numerical value of N minute is determined by the metering cycle of electric energy system.

Because DCS and CEMS data as measurement standard, so DCS and CEMS data just calculate invalid denitration electricity proportion in total period electricity, because Data Source is consistent, therefore can not can eliminate systematic error; The accurate electric quantity data utilizing this weight/power ratio to obtain with electric energy system again combines thus obtains more accurate invalid denitration electricity.

5) denitration electricity volume is calculated, denitration electricity volume=total electricity-invalid denitration electricity.

The electrical network of the embodiment of the present invention utilizes the calculating of DCS and CEMS acquisition system and electric energy system cooperative achievement thermal power plant denitration electricity volume.

As shown in Figure 1, be thermal power plant's SCR denitration technological process.Flue gas is through inlet flue gas baffle plate, to denitration facility (denitrating system), and exiting flue gas baffle plate, then through flue gas heater, desulfurization island to chimney breast, is provided with bypass gas baffle between the import of denitration facility and outlet; The denitration information gathered is needed to see attached list 1.

Above embodiment is well for electrical network solves the different problem of online price of thermal power plant's effective denitration electricity and invalid denitration electricity.

Subordinate list 1: point position and definition

Measuring point is numbered	Position	Definition	Unit	Remarks
					1	Chimney entrance	Flue gas flow after conversion ①	km 3/h	Indispensable measuring point

2	Chimney entrance	NOx concentration after conversion ②	mg/m 3	Indispensable measuring point
					3	Chimney entrance	Flue gas oxygen content	％	Suggestion measuring point
4	Chimney entrance	Flue-gas temperature	℃	Suggestion measuring point
					5	Chimney entrance	Flue gas pressures	Pa	Suggestion measuring point
6	Chimney entrance	Humidity of flue gas	％	Suggestion measuring point
					7	A side SCR entrance	NOx concentration after conversion ②	mg/m 3	Suggestion measuring point
8	A side SCR entrance	Flue gas oxygen content	％	Suggestion measuring point
					9	A side SCR entrance	Flue-gas temperature	℃	Suggestion measuring point
10	A side SCR entrance	Flue gas pressures	Pa	Suggestion measuring point
					11	B side SCR entrance	NOx concentration after conversion ②	mg/m 3	Suggestion measuring point
12	B side SCR entrance	Flue gas oxygen content	％	Suggestion measuring point
					13	B side SCR entrance	Flue-gas temperature	℃	Suggestion measuring point
14	B side SCR entrance	Flue gas pressures	Pa	Suggestion measuring point
					15	A side SCR exports	NOx concentration after conversion ②	mg/m 3	Suggestion measuring point
16	A side SCR exports	Flue gas oxygen content	％	Suggestion measuring point
					17	A side SCR exports	Flue-gas temperature	℃	Suggestion measuring point
18	A side SCR exports	Flue gas pressures	Pa	Suggestion measuring point
					19	A side SCR exports	Humidity of flue gas	％	Suggestion measuring point
20	A side SCR exports	NH 3Escape concentration	mg/m 3	Suggestion measuring point
					21	B side SCR exports	NOx concentration after conversion ②	mg/m 3	Suggestion measuring point
22	B side SCR exports	Flue gas oxygen content	％	Suggestion measuring point
					23	B side SCR exports	Flue-gas temperature	℃	Suggestion measuring point
24	B side SCR exports	Flue gas pressures	Pa	Suggestion measuring point
					25	B side SCR exports	Humidity of flue gas	％	Suggestion measuring point
26	B side SCR exports	NH 3Escape concentration	mg/m 3	Suggestion measuring point
					27	Denitrfying agent conveyance conduit	Denitrfying agent flow (conversion is to mark state)	m 3/h	Indispensable measuring point
28	SCR bypass A side shield	Damper status ③④		Indispensable measuring point
					29	SCR bypass B side shield	Damper status ③④		Indispensable measuring point
30	SCR entrance A side shield	Damper status ④		Indispensable measuring point
					31	SCR entrance B side shield	Damper status ④		Indispensable measuring point
32	SCR exports A side shield	Damper status ④		Indispensable measuring point
					33	SCR exports B side shield	Damper status ④		Indispensable measuring point
34	Machine set outlet	Unit electricity volume	Ten thousand kWh	Indispensable measuring point
					35	Transformer unit high-pressure side	Unit active power	MW	Indispensable measuring point

Note: 1. conversion refers to that conversion is to butt mark state and 6%O ₂under state;

2. conversion refers to NO ₂meter conversion is to butt mark state and 6%O ₂under state;

3. for the unit having SCR bypass;

4. none-disk terminal unit damper status is not needed to gather;

1. 2. in involved measured value, scene also can directly adopt virtual condition numerical value, gathers flue-gas temperature, pressure, water capacity and oxygen level parameter simultaneously and converts voluntarily.

Claims (3)

1. the computing method of thermal power plant's denitration electricity volume, is characterized in that, comprise the following steps:

1) calculate the denitrification apparatus NOx amount of removing: the NOx concentration before utilizing flue gas discharge continuous monitoring system Real-time Collection thermal power plant denitrification apparatus and after denitrification apparatus and flue gas flow data, calculate the NOx amount of removing as follows:

The NOx amount of removing (kg/h)=0.001 × ((SCR import NOx mean concentration (mg/Nm ³)-SCR outlet NOx mean concentration (mg/Nm ³)) × exhaust gas volumn (kNm ³/ h);

2) the theoretical minimum input amount of denitrfying agent is calculated: utilize the flue gas flow in thermal power plant's dcs and flue gas discharge continuous monitoring system collection unit running process, generate the NOx concentration of flue gas, the NOx simultaneously specified according to GB13223-2011 allows discharge value, calculates the theoretical minimum input amount of denitrfying agent;

3) determine whether effective denitration according to the real time data of calculated amount and collection, the index of effective denitration is:

A) the NOx amount of removing of denitrification apparatus is less than denitrification apparatus design capacity;

B) utilize thermal power plant dcs to gather desulfurizing agent flow in unit running process, and meet denitrfying agent flow and be greater than the theoretical minimum input amount of denitrfying agent;

C) denitration outlet NOx concentration is less than GB13223-2011 requirement;

D) utilize thermal power plant's dcs to gather denitrification apparatus damper status in unit running process, and meet SCR reactor outlet, inlet baffle standard-sized sheet;

If thermal power unit operation meets above-mentioned requirements in timing statistics section simultaneously, then the discharge of fired power generating unit flue gas NOx is qualified, and denitration electricity counts effective denitration electricity;

If thermal power unit operation does not meet above-mentioned any one requirement in timing statistics section, then the discharge of fired power generating unit flue gas NOx is defective, and denitration electricity counts invalid denitration electricity;

4) calculate invalid denitration electricity, the electricity volume being in the unit of invalid denitration state is defined as invalid denitration electricity; Calculating fee of electric energy system gathers electric quantity data with every N minute interval, dcs with level second interval harvester group active power, simultaneously according to step 4) judge denitration state, and then calculate invalid denitration electricity, wherein, N is not more than 60 minutes;

5) denitration electricity volume is calculated, denitration electricity volume=total electricity-invalid denitration electricity.

2. the computing method of thermal power plant according to claim 1 denitration electricity volume, is characterized in that: described step 2) calculate the theoretical minimum input amount of denitrfying agent and adopt and obtain with the following method:

The theoretical minimum input amount of denitrfying agent ammonia flow is determined by following formula:

$Q_{\min }=V_m\×F_{\mathrm{ch}}\×\frac{{\mathrm{NOx}}_{\mathrm{in}}-{\mathrm{NOx}}_{\max }}{M_{\mathrm{NO}2}}\×{\mathrm{\ξ}}_1\×{\mathrm{\ξ}}_2\×{\mathrm{\ξ}}_3\×{10}^{-3}---\left(1\right)$

In formula: Q _min---denitrfying agent flow theory minimum value under standard state, m ³/ h;

V _m---the molar volume of gas under standard state, value equals 22.4, L/mol;

NOx _in---with NO ₂meter, at butt mark state and 6%O ₂under state, unit SCR import NOx emission concentration, mg/m ³;

F _ch---at butt mark state and 6%O ₂under state, the total flue gas flow of unit chimney entrance, km ³/ h;

M _nO2---NO ₂molal weight, g/mol;

NOx _max---the NOx emission concentration that GB13223 allows, mg/m ³;

ξ ₁---denitrfying agent flow measurement Ratio for error modification;

ξ ₂---flue gas flow measuring error correction factor;

ξ ₃---nitrous oxides concentration measuring error update the system.

3. the computing method of thermal power plant according to claim 1 denitration electricity volume, is characterized in that: described step 4) in calculate invalid denitration electricity be adopt to obtain with the following method:

Calculating fee of electric energy system gathers electric quantity data with every N minute interval, adopts the invalid denitration electricity D in the every N of following formulae discovery minute:

$D=\frac{\underset{\mathrm{ti}}{\mathrm{\Σ}}{\∫}_0^{\mathrm{ti}}{P1}_t\mathrm{dt}}{{\∫}_0^N{P}_t\mathrm{dt}}\×E_N---\left(2\right)$

Wherein:

P1 _t---the unit obtained by data processing is in instantaneous power during invalid denitration state;

P _t---from the unit instantaneous power that denitration RTU collects;

T _i---unit is in the duration of invalid denitration state;

E _n---from the every N of the unit minute electricity that calculating fee of electric energy system obtains.